Zinc bioleaching from an iron concentrate using Acidithiobacillus ferrooxidans strain from Hercules Mine of Coahuila,Mexico

The iron concentrate from Hercules Mine of Coahuila,Mexico,which mainly contained pyrite and pyrrhotite,was treated by the bioleaching process using native strain Acidithiobacillus ferrooxidans （A.ferrooxidans） to determine the ability of these bacteria on the leaching of zinc.The native bacteria were isolated from the iron concentrate of the mine.The bioleaching experiments were carried out in shake flasks to analyze the effects of pH values,pulp density,and the ferrous sulfate concentration on the bioleaching process.The results obtained by microbial kinetic analyses for the evaluation of some aspects of zinc leaching show that the native bacteria A.ferrooxidans,which is enriched with a 9K Silverman medium under the optimum conditions of pH 2.0,20 g/L pulp density,and 40 g/L FeSO4,increases the zinc extraction considerably observed by monitoring during15 d,i.e.,the zinc concentration has a decrease of about 95% in the iron concentrate.

Anatomical variation of five plant species along an elevation gradient in Mexico City basin within the Trans-Mexican Volcanic Belt, Mexico

Change in environmental conditions with altitudinal gradients induces morpho-anatomical variations in plants that have been poorly documented in intertropical regions. Five species with three life forms, cryptophyte(Alchemilla procumbens, Geranium seemannii), hemicryptophyte(Acaena elongata, Lupinus montanus), and phanerophyte(Symphoricarpos microphyllus), distributed along an altitudinal gradient in the Sierra Nevada of central Mexico, were studied. The aims were to identify and evaluate their morpho-anatomical modifications under the hypothesis that the sizes of individuals and of their wood and leaf cell types decrease as elevation increases. Three individuals per species per site were collected at seven locations along the altitudinal gradient(2949-3952 m). Their morpho-anatomical characters were analyzed through multiple regression analyses. Elevation was the variable that best explained anatomical changes in the leaf and wood ofthe five species. Canopy density and potassium content in the soil also contributed to explain the variation in anatomical variables along the gradient. As elevation increased a bimodal pattern was observed in various anatomical characters as in the leaf width of A. elongata, A. procumbens and G. seemannii and in the vessel diameter of A. procumbens, G. seemannii, and L. montanus. Other features as the vessel diameter of A. elongata, the fiber length of S. microphyllus, and the ray width of A. elongata increased as the elevation increased. Anatomical traits have a tendency to decrease in size but just toward the end of the gradient, which is probably related to changes in canopy density. The plant response to the altitudinal gradient is more focused on anatomical adaptations than morphological variation; it is also species dependent.

Langmuir Probe and Optical Emission Spectroscopy Studies of Low-Pressure Gas Mixture of CO_2 and N_2

Optical emission spectroscopy was used to study a gas mixture glow discharge of CO2 and N2 at a total pressure of 1.2 Torr, a power of 100 W and a flow of 16.5 L/min. The emission bands were measured in the wavelength range of 200 nm to 900 nm. The principal species observed were O2^＋ （A^2П→ X^2П）, CO^＋ （A^2П→X^2∑）, N2^＋ （B^2∑u＋ → X^2∑g^＋）, CO2^＋ （A^2∏ → X^2∏）, N2（C^3∏u → B^3∏g）, O2（b^1∑g^＋→ X^3∑g^-）, and CO （a^r3∑→a^3∏）. The behavior of the band intensities as a function of the N2 percentage is consistent with recent Monte Carlo simulations. The electron temperature and ion density were determined by a double Langmuir probe. The electron temperature was found in the range of 1.55 eV to 2.93 eV, and the electron concentration in the order of 10^10 cm^-3. The electron temperature and ion density at pure N2 and pure CO2 agree with previous measurements.

Kinetic study of austenite formation during continuous heating of unalloyed ductile iron

The austenite formation kinetics in unalloyed cast ductile iron was studied on the basis of dilatometry measurements, and Avrami＇s equation was used to estimate the material＇s kinetic parameters. A continuous heating transformation diagram was constructed us-ing heating rates in the range of 0.06 to 0.83℃·s^-1. As the heating rate was augmented, the critical temperatures, c1A and Aα, as well as the intercritical range, which was evaluated as the difference between the critical temperatures, α c1Δ T =A_a- A_c1 , increased. At a low heating rate, the kinetics of austenite formation was slow as a consequence of the iron＇s silicon content. The effect of heating rate on k and n, the kinetic parameters of Avrami＇s equation, was also determined. Parameter n, which is associated with nucleation sites and growth geometry, de-creased with an increase in heating rate. In addition, parameter k increased with the increase of heating rate, suggesting that the nucleation and growth rates are carbon-and silicon-diffusion controlled during austenite formation under continuous heating.

Effect of initial microstructure on austenite formation kinetics in high-strength experimental microalloyed steels

Austenite formation kinetics in two high-strength experimental microalloyed steels with different initial microstructures comprising bainite-martensite and ferrite-martensite/austenite microconstituents was studied during continuous heating by dilatometric analysis. Austenite formation occurred in two steps： （1） carbide dissolution and precipitation and （2） transformation of residual ferrite to austenite. Dilatometric analysis was used to determine the critical temperatures of austenite formation and continuous heating transformation diagrams for heating rates ranging from 0.03°C.s^-1 to 0.67°C.s^-1. The austenite volume fraction was fitted using the Johnson-Mehl-Avrami-Kolmogorov equation to determine the kinetic parameters k and n as functions of the heating rate. Both n and k parameters increased with increasing heat- ing rate, which suggests an increase in the nucleation and growth rates of austenite. The activation energy of austenite formation was determined by the Kissinger method. Two activation energies were associated with each of the two austenite formation steps. In the first step, the austenite growth rate was controlled by carbon diffusion from carbide dissolution and precipitation; in the second step, it was controlled by the dissolution of residual ferrite to austenite.

Simulation of Modes of Ionosphere Alfven Resonator with High Quality Factors in the Case of Oblique Geomagnetic Field

The properties of the ionosphere Alfvén resonator (IAR) in the general case of an oblique geomagnetic field are investigated. The modes at the frequencies f = 0.2 - 10 Hz well localized within the ionosphere are considered, which are important for the lithosphere—ionosphere coupling. An attention is paid to the modes with quite high quality factors , where . A proper selection of calculated eigenfrequencies has been realized. Two independent simulation algorithms have been proposed. The resonant frequencies and the profiles of magnetic field components of the modes have been calculated. The modulation of electron and ion concentrations at the heights 170 - 230 km leads to essential shifting the resonant frequencies.

Asphaltene Surface Erosion in Air Plasma

Optical emission spectroscopy was applied for plasma characterization during erosion of substrates of asphaltene. The amount of 100 mg of asphaltene was carefully applied to an electrode and exposed to air plasma glow discharge at a pressure of 1.0 Tort. The plasma was generated in a stainless steel discharge chamber by an AC generator with a frequency of 60 Hz and an output power of about 60 W. The electron temperature was found to be 6.88 eV, and the ion density is about 3.5×10^16 cm^-3. As the asphaltene was exposed to the air plasma, the surface was etched. The emission from molecular bands CS2,O3, N2^＋, NO, O2, CS, S2, CN, C7H7, C2, H2, C2^-, NiO, N2 and SO, and atomic line O, were observed and some of them were used to monitor the evolution of asphaltene erosion. The asphaltene weight was reduced gradually with an etching rate of about 0.844 mg/min, during the first 20 min.

Asphaltene Erosion Process in Air Plasma: Emission Spectroscopy and Surface Analysis for Air-Plasma Reactions

Optical emission spectroscopy （OES） was applied for plasma characterization during the erosion of asphaltene substrates. An amount of 100 mg of asphaltene was carefully applied to an electrode and exposed to air-plasma glow discharge at a pressure of 1.0 Torr. The plasma was generated in a stainless steel discharge chamber by an ac generator at a frequency of 60 Hz, output power of 50 W and a gas flow rate of 1.8 L/min. The electron temperature and ion density were estimated to be 2.15±0.11 eV and （1.24±0.05）× 10^16 m^-3, respectively, using a double Langmuir probe. OES was employed to observe the emission from the asphaltene exposed to air plasma. Both molecular band emission from N2, N2＋, OH, CH, NH, O2 as well as CN, and atomic light emission from V and Hγ were observed and used to monitor the evolution of asphaltene erosion. The asphaltene erosion was analyzed with the aid of a scanning electron microscope （SEM） equipped with an energy dispersive X-ray （EDX） detector. The EDX analysis showed that the time evolution of elements C, O, S and V were similar and the chemical composition of the exposed asphaltenes remained constant. Particle size evolution was measured, showing a maximum size of 2307 μm after 60 min. This behavior is most likely related to particle agglomeration as a function of time.

How Do Physicists Create Time？

In the first part of this paper, different perspectives of time proposed in Aristotle＇s philosophy of nature, classic mechanics, thermodynamics, and the theory of relativity, will be presented. Later on, we explore the phenomenological approach of duration by Henri Bergson and Mauro Dorato＇s naturalistic proposal, which defines the ＂present＂ moment based on neuroscientific experiments. In the second part of the paper, the topic of scientific creativity is introduced, paying particular attention to David Bohm＇s ideas. Finally, the previously analysed perspectives are used to answer the following question： How do physicists create time？

Diffuse Large B-Cell Lymphoma with Anaplastic Clear Cells: A Rare Variant

Introduction: Diffuse Large B-Cell Lymphoma (DLBCL) is a heterogeneous group conformed by morphological and clinical varieties of neoplasms;it originates from peripheral B-cells and is distinguished into three groups: germinal center (GC), activated B lymphocyte (ABL), and the third type. The existence of DLBCL with anaplastic morphology and expression of CD30 without t (2;5) translocation is rare. The aim of the present article is to describe this morphologic variant in a 54-year-old woman and a 74-year-old man, respectively. Materials and Methods: Patients diagnosed with DLBCL with anaplastic variant were identified from the surgical pathology records. Results: Out of 357 biopsies with this diagnosis, 11 (3%) corresponded to the anaplastic variant, 2 presented morphological clear cells;they became visible because of an increase in volume in the cervical area of 4 months of evolution, usually associated to diaphoresis and weight loss with clinical fulminating progression. An autopsy study was performed to one patient and it showed infiltration in supraclavicular lymph nodes, thyroid, and lung. The neoplastic cells presented abundant clear cytoplasm and pleomorphic nuclei that expressed CD20, CD30 and CD45. Conclusion: This variation is rare. The clinical presentation and prognosis are controversial;we present the morphological and immunophenotype changes of this variant. The differential diagnosis from other clear cell neoplasms should be made.