1,209 research outputs found
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A study of the antioxidant capacity of oak wood used in wine ageing and the correlation with polyphenol composition
The antioxidant capacity of oak wood used in the ageing of wine was studied by four different methods: measurement of scavenging capacity against a given radical (ABTS, DPPH), oxygen radical absorbance capacity (ORAC) and the ferric reducing antioxidant power (FRAP). Although, the four methods tested gave comparable results for the antioxidant capacity measured in oak wood extracts, the ORAC method gave results with some differences from the other methods. Non-toasted oak wood samples displayed more antioxidant power than toasted ones due to differences in the polyphenol compositon. A correlation analysis revealed that ellagitannins were the compounds mainly responsible for the antioxidant capacity of oak wood. Some phenolic acids, mainly gallic acid, also showed a significant correlation with antioxidant capacity
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Time-resolved gas-phase kinetic and quantum chemical studies of the reaction of silylene with oxygen
Time-resolved kinetic studies of the reaction of silylene, SiH2, generated by laser flash photolysis of phenylsilane, have been carried out to obtain rate constants for its bimolecular reaction with O-2. The reaction was studied in the gas phase over the pressure range 1-100 Torr in SF6 bath gas, at five temperatures in the range 297-600 K. The second order rate constants at 10 Torr were fitted to the Arrhenius equation: log(k/cm(3) molecule(-1) s(-1)) = (-11.08 +/- 0.04) + (1.57 +/- 0.32 kJ mol(-1))/RT ln10 The decrease in rate constant values with increasing temperature, although systematic is very small. The rate constants showed slight increases in value with pressure at each temperature, but this was scarcely beyond experimental uncertainty. From estimates of Lennard-Jones collision rates, this reaction is occurring at ca. 1 in 20 collisions, almost independent of pressure and temperature. Ab initio calculations at the G3 level backed further by multi-configurational (MC) SCF calculations, augmented by second order perturbation theory (MRMP2), support a mechanism in which the initial adduct, H2SiOO, formed in the triplet state (T), undergoes intersystem crossing to the more stable singlet state (S) prior to further low energy isomerisation processes leading, via a sequence of steps, ultimately to dissociation products of which the lowest energy pair are H2O + SiO. The decomposition of the intermediate cyclo-siladioxirane, via O-O bond fission, plays an important role in the overall process. The bottleneck for the overall process appears to be the T -> S process in H2SiOO. This process has a small spin orbit coupling matrix element, consistent with an estimate of its rate constant of 1 x 10(9) s(-1) obtained with the aid of RRKM theory. This interpretation preserves the idea that, as in its reactions in general, SiH2 initially reacts at the encounter rate with O-2. The low values for the secondary reaction barriers on the potential energy surface account for the lack of an observed pressure dependence. Some comparisons are drawn with the reactions of CH2 + O-2 and SiCl2 + O-2
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Sustainable NGO/CBO agricultural marketing initiatives. Proceedings of a workshop held at White Field, Bangalore, 24-25 September, 2001 (NRI report no. 2660)
Restoring the sting to metric preheating
The relative growth of field and metric perturbations during preheating is
sensitive to initial conditions set in the preceding inflationary phase. Recent
work suggests this may protect super-Hubble metric perturbations from resonant
amplification during preheating. We show that this possibility is fragile and
sensitive to the specific form of the interactions between the inflaton and
other fields. The suppression is naturally absent in two classes of preheating
in which either (1) the vacua of the non-inflaton fields during inflation are
deformed away from the origin, or (2) the effective masses of non-inflaton
fields during inflation are small but during preheating are large. Unlike the
simple toy model of a coupling, most realistic particle
physics models contain these other features. Moreover, they generically lead to
both adiabatic and isocurvature modes and non-Gaussian scars on super-Hubble
scales. Large-scale coherent magnetic fields may also appear naturally.Comment: 6 pages, 3 ps figures, RevTex, revised discussion of backreaction and
new figure. To appear Phys. Rev. D (Rapid Communication
Fano resonance in electronic transport through a quantum wire with a side-coupled quantum dot: X-boson treatment
The transport through a quantum wire with a side coupled quantum dot is
studied. We use the X-boson treatment for the Anderson single impurity model in
the limit of . The conductance presents a minimum for values of T=0
in the crossover from mixed-valence to Kondo regime due to a destructive
interference between the ballistic channel associated with the quantum wire and
the quantum dot channel. We obtain the experimentally studied Fano behavior of
the resonance. The conductance as a function of temperature exhibits a
logarithmic and universal behavior, that agrees with recent experimental
results.Comment: 6 pages, 10 eps figs., revtex
Titration of submonolayer Au growth on Si(111)
Quantum Matter and Optic
Low-scale Quintessential Inflation
In quintessential inflationary model, the same master field that drives
inflation becomes, later on, the dynamical source of the (present) accelerated
expansion. Quintessential inflationary models require a curvature scale at the
end of inflation around in order to explain the large scale
fluctuations observed in the microwave sky. If the curvature scale at the end
of inflation is much smaller than , the large scale adiabatic
mode may be produced thanks to the relaxation of a scalar degree of freedom,
which will be generically denoted, according to the recent terminology, as the
curvaton field. The production of the adiabatic mode is analysed in detail in
the case of the minimal quintessential inflationary model originally proposed
by Peebles and Vilenkin.Comment: 25 pages; 5 figure
Singular Short Range Potentials in the J-Matrix Approach
We use the tools of the J-matrix method to evaluate the S-matrix and then
deduce the bound and resonance states energies for singular screened Coulomb
potentials, both analytic and piecewise differentiable. The J-matrix approach
allows us to absorb the 1/r singularity of the potential in the reference
Hamiltonian, which is then handled analytically. The calculation is performed
using an infinite square integrable basis that supports a tridiagonal matrix
representation for the reference Hamiltonian. The remaining part of the
potential, which is bound and regular everywhere, is treated by an efficient
numerical scheme in a suitable basis using Gauss quadrature approximation. To
exhibit the power of our approach we have considered the most delicate region
close to the bound-unbound transition and compared our results favorably with
available numerical data.Comment: 14 pages, 5 tables, 2 figure
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