15,123 research outputs found
Bouncing solutions from generalized EoS
We present an exact analytical bouncing solution for a closed universe filled
with only one exotic fluid with negative pressure, obeying a Generalized
Equations of State (GEoS) of the form , where
, and are constants. In our solution and
and is kept as a free parameter. For particular values of
the initial conditions, we obtain that our solution obeys Null Energy Condition
(NEC), which allows us to reinterpret the matter source as that of a real
scalar field, , with a positive kinetic energy and a potential .
We compute numerically the scalar field as a function of time as well as its
potential , and find an analytical function for the potential that
fits very accurately with the numerical results obtained. The shape of this
potential can be well described by a Gaussian-type of function, and hence,
there is no spontaneous symmetry minimum of . We further show that the
bouncing scenario is structurally stable under small variations of the
parameter , such that a family of bouncing solutions can be find
numerically, in a small vicinity of the value .Comment: 12 pages, 12 figure
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
Water vapor and silicon monoxide maser observations in the protoplanetary nebula OH 231.8+4
OH 231.8+4.2 is a well studied preplanetary nebula (pPN) around a binary
stellar system that shows a remarkable bipolar outflow. To study the structure
and kinematics of the inner 10-80 AU nebular regions we performed
high-resolution observations of the HO 6--5 and SiO
=2, =1--0 maser emissions with the Very Long Baseline Array. The absolute
position of both emission distributions were recovered using the phase
referencing technique, and accurately registered in HST optical images. HO
maser clumps are found to be distributed in two areas of 20 mas in size
spatially displaced by 60 milli-arcseconds along an axis oriented nearly
north-south. SiO masers are tentatively found to be placed between the two
HO maser emitting regions, probably indicating the position of the Mira
component of the system. The SiO maser emission traces an inner equatorial
component with a diameter of 12 AU, probably a disk rotating around the M-type
star. Outwards, we detect in the HO data a pair of polar caps, separated by
80 AU. We believe that the inner regions of the nebula probably have been
altered by the presence of the companion, leading to an equator-to-pole density
contrast that may explain the lack of HO masers and strong SiO maser
emission in the denser, equatorial regions.Comment: 5 pages, 1 figure, A&A accepte
Incremental and Modular Context-sensitive Analysis
Context-sensitive global analysis of large code bases can be expensive, which
can make its use impractical during software development. However, there are
many situations in which modifications are small and isolated within a few
components, and it is desirable to reuse as much as possible previous analysis
results. This has been achieved to date through incremental global analysis
fixpoint algorithms that achieve cost reductions at fine levels of granularity,
such as changes in program lines. However, these fine-grained techniques are
not directly applicable to modular programs, nor are they designed to take
advantage of modular structures. This paper describes, implements, and
evaluates an algorithm that performs efficient context-sensitive analysis
incrementally on modular partitions of programs. The experimental results show
that the proposed modular algorithm shows significant improvements, in both
time and memory consumption, when compared to existing non-modular, fine-grain
incremental analysis techniques. Furthermore, thanks to the proposed
inter-modular propagation of analysis information, our algorithm also
outperforms traditional modular analysis even when analyzing from scratch.Comment: 56 pages, 27 figures. To be published in Theory and Practice of Logic
Programming. v3 corresponds to the extended version of the ICLP2018 Technical
Communication. v4 is the revised version submitted to Theory and Practice of
Logic Programming. v5 (this one) is the final author version to be published
in TPL
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
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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