Phase diagram of a generalized Winfree model.

We study the phase diagram of a generalized Winfree model. The modification is such that the coupling depends on the fraction of synchronized oscillators, a situation which has been noted in some experiments on coupled Josephson junctions and mechanical systems. We let the global coupling k be a function of the Kuramoto order parameter r through an exponent z such that z=1 corresponds to the standard Winfree model, z<1 strengthens the coupling at low r (low amount of synchronization), and at z>1 , the coupling is weakened for low r . Using both analytical and numerical approaches, we find that z controls the size of the incoherent phase region and that one may make the incoherent behavior less typical by choosing z<1 . We also find that the original Winfree model is a rather special case; indeed, the partial locked behavior disappears for z>1 . At fixed k and varying gamma , the stability boundary of the locked phase corresponds to a transition that is continuous for z<1 and first order for z>1 . This change in the nature of the transition is in accordance with a previous study of a similarly modified Kuramoto model.

Steady-state visual evoked potentials and phase synchronization in migraine patients.

We investigate phase synchronization in EEG recordings from migraine patients. We use the analytic signal technique, based on the Hilbert transform, and find that migraine brains are characterized by enhanced alpha band phase synchronization in the presence of visual stimuli. Our findings show that migraine patients have an overactive regulatory mechanism that renders them more sensitive to external stimuli.

Phase shifts of synchronized oscillators and the systolic-diastolic blood pressure relation.

We study the phase-synchronization properties of systolic and diastolic arterial pressure in healthy subjects. We find that delays in the oscillatory components of the time series depend on the frequency bands that are considered, in particular we find a change of sign in the phase shift going from the very low frequency band to the high frequency band. This behavior should reflect a collective behavior of a system of nonlinear interacting elementary oscillators. We prove that some models describing such systems, e.g., the Winfree and the Kuramoto models, offer a clue to this phenomenon. For these theoretical models there is a linear relationship between phase shifts and the difference of natural frequencies of oscillators and a change of sign in the phase shift naturally emerges.

Diluted neural networks with adapting and correlated synapses.

We consider the dynamics of diluted neural networks with clipped and adapting synapses. Unlike previous studies, the learning rate is kept constant as the connectivity tends to infinity: the synapses evolve on a time scale intermediate between the quenched and annealing limits and all orders of synaptic correlations must be taken into account. The dynamics is solved by mean-field theory, the order parameter for synapses being a function. We describe the effects, in the double dynamics, due to synaptic correlations.

Chaos in neural networks with a nonmonotonic transfer function.

Time evolution of diluted neural networks with a nonmonotonic transfer function is analytically described by flow equations for macroscopic variables. The macroscopic dynamics shows a rich variety of behaviors: fixed-point, periodicity, and chaos. We examine in detail the structure of the strange attractor and in particular we study the main features of the stable and unstable manifolds, the hyperbolicity of the attractor, and the existence of homoclinic intersections. We also discuss the problem of the robustness of the chaos and we prove that in the present model chaotic behavior is fragile (chaotic regions are densely intercalated with periodicity windows), according to a recently discussed conjecture. Finally we perform an analysis of the microscopic behavior and in particular we examine the occurrence of damage spreading by studying the time evolution of two almost identical initial configurations. We show that for any choice of the parameters the two initial states remain microscopically distinct.

[Use of polyethylene glycol in the treatment of puerperal constipation]. / Uso del Polietilen Glicol como tratamiento del estreñimiento asociado al puerperio.

We evaluated the efficiency of polyethylene glycol at low dosage as a treatment for constipation in the puerperium. A prospective, open label and control study was performed in 225 puerpery patients. We observed a 94.7% of study group patients and a 10.7% of a control group patients had a evacuation in the first 48 hours, (p < 0.01). Decreased consistency of the stools was seen in the PEG group (74.3%). According to our findings, low doses of PEG were useful and safe as a treatment for constipation in the puerperium, without side effects.

Preeclampsia and calcium adenosine triphosphatase activity of red blood cell ghosts.

OBJECTIVE: The current work was undertaken to study the calcium adenosine triphosphatase activity of red blood cell membranes from pregnant women with preeclampsia. STUDY DESIGN: Six normotensive and six preeclamptic pregnant women at 38 to 39 weeks of gestation were studied. The diagnosis of preeclampsia was made on the basis of blood pressure (> 140/90 mm Hg), proteinuria (> 0.5 gm of urinary protein per day), or edema. Hemoglobin-free red blood cell ghosts were prepared from the heparinized blood samples and were used to determine the calcium adenosine triphosphatase activity. RESULTS: It was found that the calcium adenosine triphosphatase activity of preeclamptic women is diminished by about 50% compared with that of normotensive pregnant women. CONCLUSION: A diminution of the calcium adenosine triphosphatase activity of erythrocytes in preeclampsia might be an indication that the in vivo activity of the calcium pump of these cells is diminished, which could, in turn, drive the cells to increase their cytoplasmic free calcium concentration.

[Value of three-dimensional measurement of the caudate lobe in the diagnosis of liver cirrhosis by ultrasound]. / Valor de la medición tridimensional del lóbulo caudado en el diagnóstico de cirrosis por ultrasonido.

To assess the changes of the caudate lobe in the sonographic diagnosis of liver cirrhosis, 96 patients were studied at the Hospital Vargas de Caracas. 27 with histologically proved cirrhosis. 43 with other disease (30 no related with liver and 13 with hepatic disease without cirrhosis, and 26 patients without clinical evidence of liver disease. The longitudinal (CL), transverse (CT), and anteroposterior (CAP) diameters of the caudate lobe and the transverse diameter of the right lobe (RL) were measured and one, two and three dimensional caudate lobe, indexes and ratios were calculated. The analysis of these criteria revealed that the ratio of the three dimensional caudate index (C13) to the right lobe diameter (C13)/RL = iCL x CT x CAP/RL was superior to all other calculated criteria.

Tensión arterial en escolares de un medio rural / Blood pressure in school children of a rural environment

La TA en pacientes pediátricos no ha sido estudiada adecuadamente en Venezuela. El presente trabajo se realizó para determinar las cifras tensionales según edad y sexo en escolares de las poblaciones rurales de El Cortijo y Los Bagres, Dtto. Sanitario No. 3, Ed. Aragua y correlacionario con peso, talla, y antecedentes familiares. La muestra fue de 184 niños (94 varones y 90 hembras), con edades entre 7 y 14 años. Se registró el primer, cuarto y quinto ruido de Korotkoff en posición acostado, sentado y de pie, con esfigmomanómetro de mercurio. No se observó diferencia significativa entre las medias aritméticas de varones y hembras. Se evidenció una correlación significativa (p<0,05) y positiva entre TA y peso en la mayoría de los casos. Las cifras de TA registrada en posición sentado fueron siempre las más bajas en ambos sexos (p<0,05). La prevalencia de lecturas elevadas en la primera medición fue de 13,6% (6,0% en varones y 7,6% en hembras, p>0,05); el 5,6% mantendrán cifras elevadas a las cuatro semanas