EVALUATION OF THE ANTIOXIDANT ACTIVITY OF THE FLAVONOIDS ISOLATED FROM HELIOTROPIUM SINUATUM RESIN USING ORACFL, DPPH AND ESR METHODOLOGIES

Indexación: Web of Science; Scielo.The antioxidant capacity has been determined for a number of flavonoid compounds from Heliotropium sinuatum, a plant that grows in arid areas in the north of Chile. The methodologies used were: ORAC(FL) (oxygen radical absorbance capacity - fluorescein), DPPH (2,2-diphenyl-2-picrylhydrazyl) bleaching and electron spin resonance (ESR). These compounds were studied in homogeneous and heterogeneous media. The results showed that the 7-o-methyleriodictiol and 3-o-methylisorhamnetin are those with the highest antioxidant capacity.http://ref.scielo.org/m82cz

Inflation with a graceful exit and entrance driven by Hawking radiation

We present a model for cosmological inflation which has a natural "turn on" and a natural "turn off" mechanism. In our model inflation is driven by the Hawking-like radiation that occurs in Friedman-Robertson-Walker (FRW) space-time. This Hawking-like radiation results in an effective negative pressure "fluid" which leads to a rapid period of expansion in the very early Universe. As the Universe expands the FRW Hawking temperature decreases and the inflationary expansion turns off and makes a natural transition to the power law expansion of a radiation dominated universe. The "turn on" mechanism is more speculative, but is based on the common hypothesis that in a quantum theory of gravity at very high temperatures/high densities Hawking radiation will stop. Applying this speculation to the very early Universe implies that the Hawking-like radiation of the FRW space-time will be turned off and therefore the inflation driven by this radiation will turn off.Comment: 19 pages, 2 figures revtex, matches PRD published versio

Probing quantum phase transition via quantum speed limit

Quantum speed limit (QSL) is the lower bound on the time required for a state to evolve to a desired final state under a given Hamiltonian evolution. Three well-known QSLs exist Mandelstam-Tamm (MT), Margolus-Levitin (ML), and dual ML (ML$^*$) bounds. We consider one-dimensional systems that undergoes delocalization-localization transition in the presence of quasiperiodic and linear potential. By performing sudden quenches across the phase boundary, we find that the exact dynamics get captured very well by QSLs. We show that the MT bound is always tighter in the short time limit for any arbitrary state, while the optimal bound for the time of orthogonalization (time required to reach the orthogonal state) depends on the choice of the initial state. Further, for extreme quenches, we prove that the MT bound remains tighter for the time of orthogonalization, and it can qualitatively describe the non-analyticity in free energy for dynamical quantum phase transition (DQPT). Finally, we also demonstrate that the localization-delocalization transition point can be exactly identified from QSLs, whose computation cost is much less compared to many other diagnostic tools.Comment: 11 page

Variations of Bi-ionic Potentials on Counterion Concentrations

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Pressure induced electride phase formation in calcium: A key to its strange high-pressure behavior

Elemental calcium (Ca), a simple metal at ambient conditions, has attracted huge interest because of its unusual high-pressure behavior in structural, electrical, and melting properties whose origin remain unsolved. Here, using a theoretical framework appropriate for describing electride phase formation, i.e., the presence of anionic electrons, we establish electride formation in Ca at a pressure as low as 8 GPa. Our analysis shows that under pressure the valence electrons of Ca localize at octahedral holes and exhibit anionic character which is responsible for its strange pressure behavior. Our calculated enthalpy and electrical resistance indicate that Ca will directly transform from an FCC-electride phase to an SC-electride phase near 30 GPa thereby avoiding the intermediate BCC phase. These findings are not limited to Ca but might hold a key to the understanding of host-guest type structures which occur in other elemental solids though at much higher pressures.Comment: 6 pages, 5 figure

Exploring process options to enhance metal dissolution in bioleaching of Indian ocean nodules

Polymetallic Indian Ocean nodules offer a lucrative resource for valuable strategic metals such as Cu, Co and Ni. A novel bioleaching process using cell-free spent growth medium from a fully-grown culture of a marine organism isolated from the nodules (Bacillus M1) dissolved about 45% Co, and 25% Cu and Ni at a the pH of 8.2 in 4 h. To enhance metal dissolution, different modifications in the bioleaching process, such as increasing the pH of the spent growth medium, carrying out leaching in multiple steps, and introducing organic reductant in the leach pulp, were investigated in this study. Increasing the initial pH of the spent growth medium to above 12 resulted in a 25-30% increase in dissolution of Cu, Co and Ni. The pKa value for the spent growth medium was observed to be in the range of 11.5-12.5. UV-visible spectroscopy of the growth medium at pH values above 10.0 suggested a change in the structure of complexing phenolic substances present therein. A four-step leaching process using the spent growth medium, each step lasting for about 4 h, was able to bring around 60% Cu and Ni and 85% Co in solution. About 85% Co, 90% Cu and 60% Ni were dissolved in two-stage leaching, in which the bioleached residue was treated with the spent growth medium from Acidithiobacillus thiooxidans in the second cycle. The effects of concentration of starch (0.1-10%) as an organic reductant to the spent growth medium were also studied. The dissolution of Cu, Co and Ni stabilized at about 80-85% at a starch concentration of 3% and did not increase much thereafter

Experimental Investigation of Lobe Coupling for Formulation of an Approximate Generalized Experimental Data Based Model

This paper presents an approach to establish operational characteristics of ball joint-lobe type coupling by performing extensive experimentation. The experimentation must perform by changing independent physical quantities of the coupling over a wide range and response data is gathered. Based on the response data, the mathematical model is formulated correlating the responses in terms of independent variables. These models can be used as a design data for this coupling. Because of complexity in kinematics and dynamics of coupling, logic based modeling is difficult for this type of coupling. This type of coupling is mainly used in harvester. Thus, this research outcome is useful in the design of mechanical transmission system of harvester. An emphasis is laid on the study of response of the coupling towards the variation in misalignment