Ultra peripheral heavy ion collisions and the energy dependence of the nuclear radius

To estimate realistic cross sections in ultra peripheral heavy ion collisions we must remove effects of strong absorption. One method to eliminate these effects make use of a Glauber model calculation, where the nucleon-nucleon energy dependent cross sections at small impact parameter are suppressed. In another method we impose a geometrical cut on the minimal impact parameter of the nuclear collision ($b_{min} > R_1 + R_2$, where $R_i$ is the radius of ion "$i$"). In this last case the effect of a possible nuclear radius dependence with the energy has not been considered in detail up to now. Here we introduce this effect showing that for final states with small invariant mass the effect is negligible. However when the final state has a relatively large invariant mass, e.g. an intermediate mass Higgs boson, the cross section can decrease up to 50%.Comment: To appear in Phys. Lett.

A dynamical gluon mass solution in Mandelstam's approximation

We discuss the pure gauge Schwinger-Dyson equation for the gluon propagator in the Landau gauge within an approximation proposed by Mandelstam many years ago. We show that a dynamical gluon mass arises as a solution. This solution is obtained numerically in the full range of momenta that we have considered without the introduction of any ansatz or asymptotic expression in the infrared region. The vertex function that we use follows a prescription formulated by Cornwall to determine the existence of a dynamical gluon mass in the light cone gauge. The renormalization procedure differs from the one proposed by Mandelstam and allows for the possibility of a dynamical gluon mass. Some of the properties of this solution, such as its dependence on $\Lambda_{QCD}$ and its perturbative scaling behavior are also discussed.Comment: 23 pages, 4 figures. Revised version with improved discussion on the renormalization procedur

Phenomenological tests for the freezing of the QCD running coupling constant

We discuss phenomenological tests for the frozen infrared behavior of the running coupling constant and gluon propagators found in some solutions of Schwinger-Dyson equations of the gluonic sector of QCD. We verify that several observables can be used in order to select the different expressions of alpha_s found in the literature. We test the effect of the nonperturbative coupling in the tau-lepton decay rate into nonstrange hadrons, in the rho vector meson helicity density matrix that are produced in the chi_{c2} --> rho rho decay, in the photon to pion transition form factor, and compute the cross sections for elastic proton-proton scattering and exclusive rho production in deep inelastic scattering. These quantities depend on the infrared behavior of the coupling constant at different levels, we discuss the reasons for this dependence and argue that the existent and future data can be used to test the approximations performed to solve the Schwinger-Dyson equations and they already seems to select one specific infrared behavior of the coupling.Comment: 15 pages, 8 figure

The small xx behavior of the gluon structure function from total cross sections

Within a QCD-based eikonal model with a dynamical infrared gluon mass scale we discuss how the small $x$ behavior of the gluon distribution function at moderate $Q^{2}$ is directly related to the rise of total hadronic cross sections. In this model the rise of total cross sections is driven by gluon-gluon semihard scattering processes, where the behavior of the small $x$ gluon distribution function exhibits the power law $xg(x,Q^2)= h(Q^2)x^{-\epsilon}$. Assuming that the $Q^{2}$ scale is proportional to the dynamical gluon mass one, we show that the values of $h(Q^2)$ obtained in this model are compatible with an earlier result based on a specific nonperturbative Pomeron model. We discuss the implications of this picture for the behavior of input valence-like gluon distributions at low resolution scales.Comment: 19 pages, 3 figures; revised version; to appear in Int. J. Mod. Phys.

Artificial receptors for artificial olfaction

Any attempt to mimic the behavior of natural olfaction is mainly based on the properties of the artificial sensor units. Since the beginning of artificial olfaction, the main requirement for sensors has been the partial crossselectivity. This trivial feature makes possible the application of the combinatorial selectivity principle to the arrays of gas sensors. The principle of cross-selectivity can actually be fulfilled by almost any kind of sensor technology. This resulted in a vast popularity of "electronic noses" and their application. However, it is important to consider the kind of the cross-selectivity offered by sensors technology. Current sensors combines together the capability of chemistry to synthesize molecules endowed with molecular recognition properties and a number of solid-state devices that actually measure the changes in some physical properties consequent to the chemical interaction event. From this point of view, it is important to consider that in practice a number of unwanted interaction can take place even if the receptor is designed to emphasize the selectivity towards a particular kind of molecule. These are mainly driven by Van der Waals forces. Most of the available transducers cannot discriminate interactions by their energy and since Van der Waals interactions are rather ubiquitous the sensors tend to be highly correlated. A scrutiny of literature on electronic noses shows that even in case of large arrays, PCA often is limited to two variables. In this presentation, these principles will be discussed considering the study case of metalloporphyrins. These are a rather versatile class of molecules whose gas sensing properties are actively exploited in Nature, for instance for the transport of molecules such as O2 and N2 in blood. The possibility to reduce the influence of common interactions will be illustrated. It has also to be considered that the reduction of correlation is necessary to increase the array size in artificial olfaction systems. Published: 16 April 201

Fetal and early neonatal interleukin-6 response

In 1998, a systemic fetal cytokine response, defined as a plasma interleukin-6 (IL-6) value above 11 pg/mL, was reported to be a major independent risk factor for the subsequent development of neonatal morbid events even after adjustments for gestational age and other confounders. Since then, the body of literature investigating the use of blood concentrations of IL-6 as a hallmark of the fetal inflammatory response syndrome (FIRS), a diagnostic marker of early-onset neonatal sepsis (EONS) and a risk predictor of white matter injury (WMI), has grown rapidly. In this article, we critically review: IL-6 biological functions; current evidence on the association between IL-6, preterm birth, FIRS and EONS; IL-6 reference intervals and dynamics in the early neonatal period; IL-6 response during the immediate postnatal period and perinatal confounders; accuracy and completeness of IL-6 diagnostic studies for EONS (according to the Standards for Reporting of Diagnostic Accuracy statement); and recent breakthroughs in the association between fetal blood IL-6, EONS, and WMI

Residential Segregation, Neighborhood Social and Physical Context in Obesity Disparities in Hispanic Preschoolers: A Conceptual Model

During the last decade, there has been a significant inclusion in obesity prevention studies from individual characteristics to household factors then neighborhood factors. The study of place in the context of early childhood obesity studies has been limited to the food and physical built environment. With the persistent disparities in the prevalence of childhood obesity, and Hispanic minorities being increasingly affected, there is a need to reexamine existing models and develop new model conceptual frameworks to examine the role of place and residential segregation in the context of race, ethnicity, social position, and socioeconomic disparities. In the context of place as a relational space linked to where young children live, play and learn, this paper conceptualizes the role of the neighborhood social and physical factors as well as organizational, household and/or individual factors as mediators of the correlation between residential segregation and obesity in Hispanic preschoolers. In the model, we also attempted to include the role of policies and programs in moderating the negative effects of racial residential segregation and resource inequalities and their interactions with the multiple factors that may contribute to childhood obesity. Recommendations for future research need are identified