17,461 research outputs found
Quantitative representation of reactivity, selectivity and site activation concepts in organic chemistry
Indexación: ScieloReactivity, selectivity and site activation are classical concepts in chemistry which are
amenable to quantitative representation, in terms of static global, local and non local density
response functions. The use of these electronic indexes describing chemical interconversion is
developed in this work along the perspective of the pioneering work conducted in Chile by the late Professor
Fernando Zuloaga, to whom this article is dedicated in memoriam. While global responses,
represented as derivatives of the electronic energy with respect to the total number of electrons
quantitatively describe the propensity of a system to interconvert into another chemical species (chemical
reactivity), the local counterparts assesses well those regions in the molecule where the reactivity
pattern dictated by the global quantities is developed (selectivity). Site activation /deactivation may
in turn be described by the variations in the local or regional patterns of reactivity, that may be
induced by solvent effects or chemical substitution. These concepts are illustrated for a series of
chemical reactions in Organic Chemistry, including electrocyclic processes, cycloadditions and
electrophilic addition reactions. Some relationships between quantitative scales of reactivity and
reaction mechanisms are discussed.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072004000100010&lang=p
An efficient protocol to perform genetic traceability of tissue and foods from Geoffroea decorticans
The quality of a DNA isolation method depends, among others, on the target tissue and the metabolites therein. Geoffroea decorticans Burkart (chanar) is a species that has nutritional and pharmacological potential. However, an effective method of DNA extraction capable of facilitating population studies and food genetic traceability has not been studied yet. The objective of the present work was to evaluate four methods of DNA extraction from leaves and chanar-based foods. The methods were evaluated based on yield, DNA purity, and molecular markers. The CCI-P (CTAB/Chloroform-Isoamylalcohol/pellet) method showed the highest yield of DNA obtained from leaves. However, the CPCI-SC (CTAB/Phenol-Chloroform-Isoamylalcohol/silica-column) method was the only one that resulted in acceptable DNA quality with both parameters (A260/A280 and A260/A230). The leaf DNA obtained with this method showed a greater amount of fragments with RAPD, and an acceptable amount of fragments with ISSR. On the other hand, the CCI-P method showed a higher yield of DNA from arrope de chanar (syrup). However, the CPCI-SC method was the only one that had relatively better DNA quality, which allowed the amplification of molecular markers. Regarding chanar flour, the CPCI-SC method showed the highest yield, DNA quality and good amplification with molecular markers. Therefore, the CPCI-SC extraction method is efficient for obtaining DNA from different matrices, and can support studies for a possible designation of origin of chanar-based foods
Holographic model for heavy vector meson masses
The experimentally observed spectra of heavy vector meson radial excitations
show a dependence on two different energy parameters. One is associated with
the quark mass and the other with the binding energy levels of the quark
anti-quark pair. The first is present in the large mass of the first state
while the other corresponds to the small mass splittings between radial
excitations. In this article we show how to reproduce such a behavior with
reasonable precision using a holographic model. In the dual picture, the large
energy scale shows up from a bulk mass and the small scale comes from the
position of anti-de Sitter (AdS) space where field correlators are calculated.
The model determines the masses of four observed S-wave states of charmonium
and six S-wave states of bottomonium with , 6.1 % rms error. In consistency
with the physical picture, the large energy parameter is flavor dependent,
while the small parameter, associated with quark anti-quark interaction is the
same for charmonium and bottomonium states.Comment: In V5 we just added some clarifying explanations about the model. 5
tables, no figure. Version published in Europhysics Letter
Non-equilibrium correlations and entanglement in a semiconductor hybrid circuit-QED system
We present a theoretical study of a hybrid circuit-QED system composed of two
semiconducting charge-qubits confined in a microwave resonator. The qubits are
defined in terms of the charge states of two spatially separated double quantum
dots (DQDs) which are coupled to the same photon mode in the microwave
resonator. We analyze a transport setup where each DQD is attached to
electronic reservoirs and biased out-of-equilibrium by a large voltage, and
study how electron transport across each DQD is modified by the coupling to the
common resonator. In particular, we show that the inelastic current through
each DQD reflects an indirect qubit-qubit interaction mediated by off-resonant
photons in the microwave resonator. As a result of this interaction, both
charge qubits stay entangled in the steady (dissipative) state. Finite shot
noise cross-correlations between currents across distant DQDs are another
manifestation of this nontrivial steady-state entanglement.Comment: Final versio
Holographic Picture of Heavy Vector Meson Melting
The fraction of heavy vector mesons produced in a heavy ion collision, as
compared to a proton proton collision, serves as an important indication of the
formation of a thermal medium, the quark gluon plasma. This sort of analysis
strongly depends on understanding the thermal effects of a medium like the
plasma on the states of heavy mesons. In particular, it is crucial to know the
temperature ranges where they undergo a thermal dissociation, or melting.
AdS/QCD models are know to provide an important tool for the calculation of
hadronic masses, but in general are not consistent with the observation that
decay constants of heavy vector mesons decrease with excitation level. It has
recently been shown that this problem can be overcome using a soft wall
background and introducing an extra energy parameter, through the calculation
of correlation functions at a finite position of anti-de Sitter space. This
approach leads to the evaluation of masses and decay constants of S wave
quarkonium states with just one flavor dependent and one flavor independent
parameters. Here we extend this more realistic model to finite temperatures and
analyse the thermal behavior of the states and of bottomonium
and charmonium. The corresponding spectral function exhibits a consistent
picture for the melting of the states where, for each flavor, the higher
excitations melt at lower temperatures. We estimate for these six states, the
energy ranges in which the heavy vector mesons undergo a transition from a well
defined peak in the spectral function to complete melting in the thermal
medium. A very clear distinction between the heavy flavors emerges, with
bottomonium state surviving deconfinemet transition at
temperatures much larger than the critical deconfinement temperature of the
medium.Comment: 20 pages, 7 figure
Decay constants in soft wall AdS/QCD revisited
Phenomenological AdS/QCD models, like hard wall and soft wall, provide
hadronic mass spectra in reasonable consistency with experimental and (or)
lattice results. These simple models are inspired in the AdS/CFT correspondence
and assume that gauge/ gravity duality holds in a scenario where conformal
invariance is broken through the introduction of an energy scale.
Another important property of hadrons: the decay constant, can also be
obtained from these models. However, a consistent formulation of an AdS/QCD
model that reproduces the observed behavior of decay constants of vector meson
excited states is still lacking. In particular: for radially excited states of
heavy vector mesons, the experimental data lead to decay constants that
decrease with the radial excitation level.
We show here that a modified framework of soft wall AdS/QCD involving an
additional dimensionfull parameter, associated with an ultraviolet energy
scale, provides decay constants decreasing with radial excitation level. In
this version of the soft wall model the two point function of gauge theory
operators is calculated at a finite position of the anti-de Sitter space radial
coordinate.Comment: Shorter (letter) version. Results unchanged. More references
included. We now explain that the large UV scale of the model is associated
with the non-hadronic decay of the heavy vector meson into light leptons.
Version Published in Phys. Lets.
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