Pyrite oxidation under initially neutral pH conditions and in the presence of Acidithiobacillus ferrooxidans and micromolar hydrogen peroxide

Hydrogen peroxide (H2O2) at a micromolar level played a role in the microbial surface oxidation of pyrite crystals under initially neutral pH. When the mineral-bacteria system was cyclically exposed to 50 μM H2O2, the colonization of Acidithiobacillus ferrooxidans onto the mineral surface was markedly enhanced, as compared to the control(no added H2O2). This can be attributed to the effects of H2O2 on increasing the roughness of the mineral surfaces, as well as the acidity and Fe2+ concentration at the mineral-solution interfaces. All of these effects tended to create more favourable nanoto micro-scale environments in the mineral surfaces for the cell adsorption. However, higher H2O2 levels inhibited the attachment of cells onto the mineral surfaces, possibly due to the oxidative stress in the bacteria when they approached the mineral surfaces where high levels of free radicals are present as a result of Fenton-like reactions. The more aggressive nature of H2O2 as an oxidant caused marked surface flaking of the mineral surface. The XPS results suggest that H2O2 accelerated the oxidation of pyrite-S and consequently facilitated the overall corrosion cycle of pyrite surfaces. This was accompanied by pH drop in the solution in contact with the pyrite cubes

Crystal growth and in-plane optical properties of Tl2_2Ba2_2Can−1_{n-1}Cun_nOx_x (n=1,2,3) superconductors

Single crystals of thallium-based cuprates with the general formula Tl$_{2}$Ba$_{2}$Ca$_{n-1}$Cu$_{n}$O$_{x}$(n=1,2,3) have been grown by the flux method. The superconducting transition temperatures determined by the ac magnetic susceptibility are 92 K, 109 K, and 119 K for n=1,2,3 respectively. X-ray diffraction measurements and EDX compositional analysis were described. We measured in-plane optical reflectance from room temperature down to 10 K, placing emphasis on Tl-2223. The reflectance roughly has a linear-frequency dependence above superconducting transition temperature, but displays a pronounced knee structure together with a dip-like feature at higher frequency below T$_c$. Correspondingly, the ratio of the reflectances below and above T$_{c}$ displays a maximum and a minimum near those feature frequencies. In particular, those features in Tl2223 appear at higher energy scale than Tl2212, and Tl2201. The optical data are analyzed in terms of spectral function. We discussed the physical consequences of the data in terms of both clean and dirty limit.Comment: 8 pages, 13 figures, to be published in Phys. Rev.

Scaling of Anisotropic Flows and Nuclear Equation of State in Intermediate Energy Heavy Ion Collisions

Elliptic flow ($v_2$) and hexadecupole flow ($v_4$) of light clusters have been studied in details for 25 MeV/nucleon $^{86}$Kr + $^{124}$Sn at large impact parameters by Quantum Molecular Dynamics model with different potential parameters. Four parameter sets which include soft or hard equation of state (EOS) with/without symmetry energy term are used. Both number-of-nucleon ($A$) scaling of the elliptic flow versus transverse momentum ($p_t$) and the scaling of $v_4/A^{2}$ versus $(p_t/A)^2$ have been demonstrated for the light clusters in all above calculation conditions. It was also found that the ratio of $v_4/{v_2}^2$ keeps a constant of 1/2 which is independent of $p_t$ for all the light fragments. By comparisons among different combinations of EOS and symmetry potential term, the results show that the above scaling behaviors are solid which do not depend the details of potential, while the strength of flows is sensitive to EOS and symmetry potential term.Comment: 5 pages, 5 figure

Scaling of nuclear modification factors for hadrons and light nuclei

The number of constituent quarks (NCQ-) scaling of hadrons and the number of constituent nucleons (NCN-) scaling of light nuclei are proposed for nuclear modification factors ($R_{cp}$) of hadrons and light nuclei, respectively, according to the experimental investigations in relativistic heavy-ion collisions. Based on coalescence mechanism the scalings are performed for pions and protons in quark level, and light nuclei $d (\bar d)$ and $^3$He for nucleonic level, respectively, formed in Au + Au and Pb + Pb collisions and nice scaling behaviour emerges. NCQ or NCN scaling law of $R_{cp}$ can be respectively taken as a probe for quark or nucleon coalescence mechanism for the formation of hadron or light nuclei in relativistic heavy-ion collisions.Comment: 6 pages, 6 figure

Temperature determined by isobaric yield ratio in heavy-ion collisions

This work focuses on the study of temperature associated with the final heavy fragments in reactions induced by both the neutron-proton symmetric and the neutron-rich projectiles, and with incident energy ranges from 60$A$ MeV to 1$A$ GeV. Isobaric yield ratio (IYR) is used to determine the temperature of heavy fragments. Cross sections of measured fragment in reactions are analyzed, and a modified statistical abrasion-ablation (SAA) model is used to calculate the yield of fragment in 140$A$ MeV $^{64}$Ni + $^{9}$Be and 1$A$ GeV $^{136}$Xe + $^{208}$Pb reactions. Relatively low $T$ of heavy fragments are obtained in different reactions ($T$ ranges from 1 to 3MeV). $T$ is also found to depend on the neutron-richness of the projectile. The incident energy affects $T$ very little. $\Delta\mu/T$ (the ratio of the difference between the chemical potential of neutron and proton to temperature) is found to increase linearly as $N/Z$ of projectile increases. It is found that $T$ of the $^{48}$Ca reaction, for which IYRs are of $A<50$ isobars, is affected greatly by the temperature-corrected $\Delta B(T)$. But $T$ of reactions using IYRs of heavier fragments are only slightly affected by the temperature-corrected $\Delta B(T)$. The SAA model analysis gives a consistent overview of the results extracted in this work. $T$ from IYR, which is for secondary fragment, is different from that of the hot emitting source. $T$ and $\Delta\mu$ are essentially governed by the sequential decay process.Comment: 7 pages, 6 figure

Reexamining the "finite-size" effects in isobaric yield ratios using a statistical abrasion-ablation model

The "finite-size" effects in the isobaric yield ratio (IYR), which are shown in the standard grand-canonical and canonical statistical ensembles (SGC/CSE) method, is claimed to prevent obtaining the actual values of physical parameters. The conclusion of SGC/CSE maybe questionable for neutron-rich nucleus induced reaction. To investigate whether the IYR has "finite-size" effects, the IYR for the mirror nuclei [IYR(m)] are reexamined using a modified statistical abrasion-ablation (SAA) model. It is found when the projectile is not so neutron-rich, the IYR(m) depends on the isospin of projectile, but the size dependence can not be excluded. In reactions induced by the very neutron-rich projectiles, contrary results to those of the SGC/CSE models are obtained, i.e., the dependence of the IYR(m) on the size and the isospin of the projectile is weakened and disappears both in the SAA and the experimental results.Comment: 5 pages and 4 figure

Isobaric yield ratio difference between the 140 AA MeV 58,64^{58, 64}Ni + 9^{9}Be reactions studied by antisymmetric molecular dynamics model

\item[Background] The isobaric yield ratio difference (IBD) method is found to be sensitive to the density difference of neutron-rich nucleus induced reaction around the Fermi energy. \item[Purpose] An investigation is performed to study the IBD results in the transport model. \item[Methods] The antisymmetric molecular dynamics (AMD) model plus the sequential decay model GEMINI are adopted to simulate the 140$A$ MeV $^{58, 64}$Ni + $^{9}$Be reactions. A relative small coalescence radius R$_c =$ 2.5 fm is used for the phase space at $t =$ 500 fm/c to form the hot fragment. Two limitations on the impact parameter ($b1 = 0 - 2$ fm and $b2 = 0 - 9$ fm) are used to study the effect of central collisions in IBD. \item[Results] The isobaric yield ratios (IYRs) for the large--$A$ fragments are found to be suppressed in the symmetric reaction. The IBD results for fragments with neutron-excess $I =$ 0 and 1 are obtained. A small difference is found in the IBDs with the $b1$ and $b2$ limitations in the AMD simulated reactions. The IBD with $b1$ and $b2$ are quite similar in the AMD + GEMINI simulated reactions. \item[Conclusions] The IBDs for the $I =$ 0 and 1 chains are mainly determined by the central collisions, which reflects the nuclear density in the core region of the reaction system. The increasing part of the IBD distribution is found due to the difference between the densities in the peripheral collisions of the reactions. The sequential decay process influences the IBD results. The AMD + GEMINI simulation can better reproduce the experimental IBDs than the AMD simulation.Comment: 6 pages, 5 figure