Estudio in vitro de la actividad citotóxica de resinas dentales tipo BIS-GMA

Las resinas composites se emplean desde hace varias décadas en distintas aplicaciones estomatológicas, volviéndose indispensables para lograr una alta calidad en los servicios modernos. Uno de los monómeros acrílicos más utilizados en estos materiales poliméricos de recubrimiento es el 2-bis-[p-(2-hidroxi-3-metacriloxipropoxi) fenil] propano, conocido comúnmente como Bis- GMA. El conocimiento de las interacciones de estos materiales con el sistema biológico es de vital importancia debido al uso tan difundido de los mismos en la práctica clínica. El comportamiento de una célula viva en contacto con un material extraño es un problema esencial en las aplicaciones biomédicas de polímeros sintéticos. Los ensayos in vitro son sistemas muy útiles para la evaluación de los efectos biológicos de los biomateriales. En el laboratorio de Inmunofarmacología del INOR se llevó a cabo la evaluación de la toxicidad de dos resinas dentales tipo Bis-GMA producidas por el Centro de Biomateriales de la Universidad de La Habana: el Obtudent Fotocurado (FC), resina fotopolimerizable para restauraciones dentales y el Cubridem Autocurado (AC), sellante dental para fosas y fisuras. Este estudio forma parte de las evaluaciones preclínicas biológicas de biomateriales y equipos médicos implantables que se lleva a cabo en Cuba a través de la Red Funcional de Implantología del Ministerio de Salud Pública. Se aplicó el método de citotoxicidad in vitro descrito por Stanley para la evaluación toxicológica de materiales dentales. Ambos composites resultaron citotóxicos para la línea de fibroblastos L929, lo que se corresponde con lo descrito en la literatura para este tipo de material. Su citotoxicidad se encontró en el rango de la de los análogos comerciales evaluados.Peer Reviewe

Quasiperiodic Patterns in Boundary-Modulated Excitable Waves

We investigate the impact of the domain shape on wave propagation in excitable media. Channelled domains with sinusoidal boundaries are considered. Trains of fronts generated periodically at an extreme of the channel are found to adopt a quasiperiodic spatial configuration stroboscopically frozen in time. The phenomenon is studied in a model for the photo-sensitive Belousov-Zabotinsky reaction, but we give a theoretical derivation of the spatial return maps prescribing the height and position of the successive fronts that is valid for arbitrary excitable reaction-diffusion systems.Comment: 4 pages (figures included

Phase Transitions in a Forest-Fire Model

We investigate a forest-fire model with the density of empty sites as control parameter. The model exhibits three phases, separated by one first-order phase transition and one 'mixed' phase transition which shows critical behavior on only one side and hysteresis. The critical behavior is found to be that of the self-organized critical forest-fire model [B. Drossel and F. Schwabl, Phys. Rev. Lett. 69, 1629 (1992)], whereas in the adjacent phase one finds the spiral waves of the Bak et al. forest-fire model [P. Bak, K. Chen and C. Tang, Phys. Lett. A 147, 297 (1990)]. In the third phase one observes clustering of trees with the fire burning at the edges of the clusters. The relation between the density distribution in the spiral state and the percolation threshold is explained and the implications for stationary states with spiral waves in arbitrary excitable systems are discussed. Furthermore, we comment on the possibility of mapping self-organized critical systems onto 'ordinary' critical systems.Comment: 30 pages RevTeX, 9 PostScript figures (Figs. 1,2,4 are of reduced quality), to appear in Phys. Rev.

Nuclear Attenuation of high energy two-hadron system in the string model

Nuclear attenuation of the two-hadron system is considered in the string model. The two-scale model and its improved version with two different choices of constituent formation time and sets of parameters obtained earlier for the single hadron attenuation, are used to describe available experimental data for the $z$-dependence of subleading hadron, whereas satisfactory agreement with the experimental data has been observed. A model prediction for $\nu$-dependence of the nuclear attenuation of the two-hadron system is also presented.Comment: 8 page

Detecting the (Quasi-)Two-Body Decays of τ\tau Leptons in Short-Baseline Neutrino Oscillation Experiments

Novel detector schemes are proposed for the short-baseline neutrino experiments of next generation, aimed at exploring the large-$\Delta m^2$ domain of \omutau oscillations in the appearance mode. These schemes emphasize good spectrometry for charged particles and for electromagnetic showers and efficient reconstruction of \ypi_gg decays. The basic elements are a sequence of relatively thin emulsion targets, immersed in magnetic field and interspersed with electronic trackers, and a fine-grained electromagnetic calorimeter built of lead glass. These elements act as an integral whole in reconstructing the electromagnetic showers. This conceptual scheme shows good performance in identifying the $\tau$ (quasi-)two-body decays by their characteristic kinematics and in selecting the electronic decays of the $\tau$.Comment: 34 pages, 8 figure

Application of a laser induced fluorescence model to the numerical simulation of detonation waves in hydrogen-oxygen-diluent mixtures

A laser-induced-fluorescence model has been implemented and used to post-process detonation wave numerical simulation results to allow a direct comparison with previous experimental visualizations of detonations in hydrogen–oxygen–diluent mixtures. The model is first applied to steady one-dimensional simulation results obtained with detailed chemistry. The effects on the fluorescence intensity of the model parameters are examined to explore the dominant processes. The dominant interference process in the experiments carried out to date is the absorption of incident laser light by the high concentration of OH in and behind the reaction zone. The model is then applied to unsteady two-dimensional simulation results obtained with reduced chemical schemes to obtain synthetic PLIF image. The results demonstrate good qualitative agreement between the experimental and calculated laser-induced-fluorescence intensities. The model limitations and the experimental uncertainties are discussed together with a critical evaluation of the modeling approach

Composites de hidroxiapatita con matrices biodegradables

Mucho se ha publicado sobre el empleo de la hídroxíapatita (HAP) como un sustituto del hueso en diferentes áreas de la medicina Desde hace algunos años, se viene criticando el uso de este sistema debido a la capacidad de migración de las partí­culas de HAP del sitio del implante. Su posible estabilización se viene investigando y se han desarrollado métodos para lograrlo. Se prepararon composites de hídroxíapatita con quitosana (CHI) y ácido acrílico (AA) con el objetivo de obtener sistemas biodegradables con características osteoconductoras. Se estudió la influencia de dife­rentes factores: método de preparación, contenido de HAP y la concentración de CID sobre la cinética de fotopolimerización de estos composites bajo irradación con luz visible. Como sistema de iniciación se empleó el par canforquinona-alcohol N,N­dirnetilaminobencílico, ambos al 1 % en peso con respecto al AA. Se encontró que el método de preparación influye sobre las propiedades fisico-quínúcas y cinéticas de los composites. Por ejemplo, para los sistemas preparados sobre la base de geles de AA y CHl previamente hinchada con agua, se observan menores velocidades de polimeriza­ción (R,) que para los composites obtenidos a partir de los llamados geles inversos, donde el AA se pone previamente en contacto con la CHI (antes de la formación de su gel con agua)

Microvolt T-Wave Alternans and the Risk of Death or Sustained Ventricular Arrhythmias in Patients With Left Ventricular Dysfunction

ObjectivesThis study hypothesized that microvolt T-wave alternans (MTWA) improves selection of patients for implantable cardioverter-defibrillator (ICD) prophylaxis, especially by identifying patients who are not likely to benefit.BackgroundMany patients with left ventricular dysfunction are now eligible for prophylactic ICDs, but most eligible patients do not benefit; MTWA testing has been proposed to improve patient selection.MethodsOur study was conducted at 11 clinical centers in the U.S. Patients were eligible if they had a left ventricular ejection fraction (LVEF) ≤0.40 and lacked a history of sustained ventricular arrhythmias; patients were excluded for atrial fibrillation, unstable coronary artery disease, or New York Heart Association functional class IV heart failure. Participants underwent an MTWA test and then were followed for about two years. The primary outcome was all-cause mortality or non-fatal sustained ventricular arrhythmias.ResultsIschemic heart disease was present in 49%, mean LVEF was 0.25, and 66% had an abnormal MTWA test. During 20 ± 6 months of follow-up, 51 end points (40 deaths and 11 non-fatal sustained ventricular arrhythmias) occurred. Comparing patients with normal and abnormal MTWA tests, the hazard ratio for the primary end point was 6.5 at two years (95% confidence interval 2.4 to 18.1, p < 0.001). Survival of patients with normal MTWA tests was 97.5% at two years. The strong association between MTWA and the primary end point was similar in all subgroups tested.ConclusionsAmong patients with heart disease and LVEF ≤0.40, MTWA can identify not only a high-risk group, but also a low-risk group unlikely to benefit from ICD prophylaxis

Photoproduction off Nuclei and Point-like Photon Interactions Part I: Cross Sections and Nuclear Shadowing

High energy photoproduction off nuclear targets is studied within the Glauber-Gribov approximation. The photon is assumed to interact as a $q\bar{q}$-system according to the Generalized Vector Dominance Model and as a ``bare photon'' in direct scattering processes with target nucleons. We calculate total cross sections for interactions of photons with nuclei taking into account coherence length effects and point-like interactions of the photon. Results are compared to data on photon-nucleus cross sections, nuclear shadowing, and quasi- elastic $\rho$-production. Extrapolations of cross sections and of the shadowing behaviour to high energies are given.Comment: 15 pages, 12 figure