2,615 research outputs found
On the zero crossing of the three-gluon vertex
We report on new results on the infrared behaviour of the three-gluon vertex
in quenched Quantum Chormodynamics, obtained from large-volume lattice
simulations. The main focus of our study is the appearance of the
characteristic infrared feature known as 'zero crossing', the origin of which
is intimately connected with the nonperturbative masslessness of the
Faddeev-Popov ghost. The appearance of this effect is clearly visible in one of
the two kinematic configurations analyzed, and its theoretical origin is
discussed in the framework of Schwinger-Dyson equations. The effective coupling
in the momentum subtraction scheme that corresponds to the three-gluon vertex
is constructed, revealing the vanishing of the effective interaction at the
exact location of the zero crossing.Comment: 6 pages, 4 figure
Instanton traces in lattice gluon correlation functions
Strong coupling constant computed in Landau gauge and MOM renormalization
scheme from lattice two and three gluon Green Functions exhibits an unexpected
behavior in the deep IR, showing a maximum value around . We
analise this coupling below this maximum within a semiclassical approach, were
gluon degrees of freedom at very low energies are described in terms of the
classical solutions of the lagrangian, namely instantons. We provide some new
results concerning the relationship between instantons and the low energy
dynamics of QCD, by analising gluon two- and three-point Green functions
separately and with the help of a cooling procedure to eliminate short range
correlations.Comment: 4 pages, talk given at XXXX Rencontres de Moriond on QCD and Hadronic
Interactions, La Thuile (Italy
Refining the detection of the zero crossing for the three-gluon vertex in symmetric and asymmetric momentum subtraction schemes
This article reports on the detailed study of the three-gluon vertex in four-dimensional SU(3) Yang-Mills theory employing lattice simulations with large physical volumes and high statistics. A meticulous scrutiny of the so-called symmetric and asymmetric kinematical configurations is performed, and it is shown that the associated form factor changes sign at a given range of momenta. The lattice results are compared to the model-independent predictions of Schwinger-Dyson equations, and a very good agreement between the two is found
Instanton liquid properties from lattice QCD
We examined the instanton contribution to the QCD configurations generated from lattice QCD for N-F = 0, N-F = 2 + 1 and NF = 2 + 1 + 1 dynamical quark flavors from two different and complementary approaches. First via the use of Gradient flow, we computed instanton liquid properties using an algorithm to localize instantons in the gauge field con figurations and studied their evolution with flow time. Then, the analysis of the running at low momenta of gluon Green\u27s functions serves as an independent confirmation of the instanton density which can also be derived without the use of the Gradient flow
A 0535+26: an X-ray/Optical Tour
We compiled X-ray and Optical observations of the accreting X-ray binary
system A 0535+262 since its discovery in 1975, that will allow us to shed light
on the unpredictable behavior of this binary system. We present the data in
terms of the Be-disk interaction with the neutron star companion. In addition,
we show recent results from the continuous monitoring of this source by the
Gamma-ray Burst Monitor(GBM), on board the Fermi observatory, since its launch
in 2008 June 11.Comment: 4 pages, 5 figures, Conference proceeding of "Astrophysics of Neutron
Stars 2010 - a conference in honor of M. Ali Alpar", 2-6 August 2010, Cesme,
Izmir, Turke
Efficiency of hydrophobic phosphonium ionic liquids and DMSO as recyclable cellulose dissolution and regeneration media
Hydrophobic, long-chain tetraalkylphosphonium acetate salts (ionic liquids) were combined with a dipolar aprotic co-solvent, dimethylsulfoxide (DMSO), and the feasibility of these solvent systems for cellulose dissolution and regeneration was studied. A 60 : 40 w/w mixture of the ionic liquid tetraoctylphosphonium acetate ([P-8888][OAc]) and DMSO was found to dissolve up to 8 wt% cellulose, whilst trioctyl(tetradecyl) phosphonium acetate ([P-14888][OAc]) dissolved up to 3 wt% cellulose. Water (an anti-solvent for cellulose) was found to give rise to biphasic liquid-liquid systems when combined with these mixtures, yielding an upper phase rich in ionic liquid and a lower aqueous phase. The liquid-liquid equilibria of the ternary systems were experimentally determined, finding that DMSO strongly partitioned towards the aqueous phase. Thus, a process scheme involving simultaneous regeneration of cellulose and recycling of the solvent system was envisioned, and demonstrated on a large scale using [P-8888] [OAc]. A large portion of the ionic liquid (ca. 60 wt%) was directly recovered via phase separation, with a further 37 wt% being recovered from the swollen cellulose phase and residual materials, bringing recovery to 97%. XRD analysis of the recovered cellulose materials showed a loss of crystallinity and conversion from Cellulose I to Cellulose II. Non-dissolving compositions of ionic liquid and DMSO did not affect cellulose crystallinity after cellulose pulp treatment.Peer reviewe
Cycle of Knowledge in the Management of the Supply Chain of Corn for Human Consumption
The objective of this study is to characterize the cycle of knowledge in the supply chain of the industry of corn for human consumption. White corn is cultivated almost exclusively for human consumption and it has a significant value in the food supply in countries whose diet has a high proportion of this variety of corn, such as: Venezuela, México and Colombia in America, and the Republic of South Africa and Sahel countries in Africa. Corn is produced in Venezuela, under rainfed conditions and in a highly mechanized production system. The cycle of knowledge is defined as a progressive spiral in which knowledge is created, stored, transferred, applied and preserved, in order to increase the competitiveness and sustainability of organizations and companies in the food supply chain. This non experimental and crosssectional research is of a descriptive type. It was conducted in Venezuela during the second semester of 2009 in the supply chain of white corn, specifically, at the level of first tier producers (primary sector). The population is constituted by 1,754 producers of corn in the most important producing regions of the country. The representative sample was selected by the stratified sampling technique with proportional allocation: by association of corn producers and according to the grain yield. A questionnaire was designed and conducted according to the structured survey method. Its validity was verified by discriminant tests of items and its reliability through Bartlett's test, variance factorial analysis, Kaiser/Meyer/Olkin and Cronbach Alpha, achieving the last one a value of 0.9276.The production units have an average area of 67.17 ha, with 1.97 permanent workers and 4.06 temporary workers. They obtained a physical productivity of 4,210.45 kg/ha. The Knowledge Index (KI) achieved a value of 69.78% and the Perception Index of the results (PI) was 76.06%. The Pearson correlation among these indices was positive and significant with a value of 0.51. The factorial analysis for principal components with rotated factors allows obtaining four factors from the five dimensions originally considered. These factors are: (1) knowledge creation, (2) knowledge storage, (3) knowledge transfer and application, and (4) preservation of knowledge.The results allow us to conclude that the cycle of knowledge is managed in four stages in an intuitive and predominantly tacit manner which is the reason why those practices related to explicit knowledge become the agents of differentiation. Moreover, the existence of a positive correlation between the Knowledge Index and the Perception Index of the positive results by the producer was also proven
La concepción de ciencia del docente en formación y su pertinencia con los desafíos actuales
Dada la naturaleza dinámica y evolutiva que ha adquirido en la actualidad el saber científico, y su repercusión directa en la tecnología y la sociedad, surge la inquietud por explorar la visión de ciencia que tienen los docentes en formación de ciencias naturales de Venezuela. Para reflexionar en torno a esto, se realizó una investigación exploratoria de carácter documental y de campo, encontrando que los docentes en formación tienen una sola visión del concepto de ciencia como método sistemático y reduccionista. Investigaciones de esta naturaleza, permiten reflexionar en torno a los cambios que requiere la formación inicial y continua de los futuros docentes, a fin de formar profesionales conscientes del valor y las relaciones entre ciencia, tecnología y sociedad, tendiendo hacia la humanización de la ciencia de acuerdo a los grandes desafíos de la sociedad del milenio
Prevalence of infection with high-risk human papillomavirus in women in Colombia
AbstractThe prevalence of human papillomavirus (HPV) infections in 2109 females inhabiting five cities of Colombia was determined. Of the 49.2% with an HPV infection, 59.8% were infected with more than one viral type. Species 7 (of the the genus Alphapapillomavirus) was associated with multiple infections. Analysis of the socio-demographic data revealed a statistically significant protective effect associated with the status of civil union (civil recognition of cohabitation without marriage), and indigenous ethnicity proved to be a risk factor for HPV infection. This is the first study comparing HPV infection among women from geographical regions of Colombia with different socio-cultural structures
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