Exploring the geometry of the bifurcation sets in parameter space.

By studying a nonlinear model by inspecting a p-dimensional parameter space through ( p - 1 ) -dimensional cuts, one can detect changes that are only determined by the geometry of the manifolds that make up the bifurcation set. We refer to these changes as geometric bifurcations. They can be understood within the framework of the theory of singularities for differentiable mappings and, in particular, of the Morse Theory. Working with a three-dimensional parameter space, geometric bifurcations are illustrated in two models of neuron activity: the Hindmarsh-Rose and the FitzHugh-Nagumo systems. Both are fast-slow systems with a small parameter that controls the time scale of a slow variable. Geometric bifurcations are observed on slices corresponding to fixed values of this distinguished small parameter, but they should be of interest to anyone studying bifurcation diagrams in the context of nonlinear phenomena.

A monocular wide-field speed sensor inspired by the crabs' visual system for traffic analysis.

The development of visual sensors for traffic analysis can benefit from mimicking two fundamental aspects of the visual system of crabs: their panoramic vision and their visual processing strategy adapted to a flat world. First, the use of omnidirectional cameras in urban environments allows for analyzing the simultaneous movement of many objects of interest over broad areas. This would reduce the costs and complications associated with infrastructure: installation, synchronization, maintenance, and operation of traditional vision systems that use multiple cameras with a limited field of view. Second, in urban traffic analysis, the objects of interest (e.g. vehicles and pedestrians) move on the ground surface. This constraint allows the calculation of the 3D trajectory of the vehicles using a single camera without the need to use binocular vision techniques.The main contribution of this work is to show that the strategy used by crabs to visually analyze their habitat (monocular omnidirectional vision with the assumption of a flat world ) is useful for developing a simple and effective method to estimate the speed of vehicles on long trajectories in urban environments. It is shown that the proposed method estimates the speed with a root mean squared error of 2.7 km h-1.

Classification of fold/hom and fold/Hopf spike-adding phenomena.

The Hindmarsh-Rose neural model is widely accepted as an important prototype for fold/hom and fold/Hopf burstings. In this paper, we are interested in the mechanisms for the production of extra spikes in a burst, and we show the whole parametric panorama in an unified way. In the fold/hom case, two types are distinguished: a continuous one, where the bursting periodic orbit goes through bifurcations but persists along the whole process and a discontinuous one, where the transition is abrupt and happens after a sequence of chaotic events. In the former case, we speak about canard-induced spike-adding and in the second one, about chaos-induced spike-adding. For fold/Hopf bursting, a single (and continuous) mechanism is distinguished. Separately, all these mechanisms are presented, to some extent, in the literature. However, our full perspective allows us to construct a spike-adding map and, more significantly, to understand the dynamics exhibited when borders are crossed, that is, transitions between types of processes, a crucial point not previously studied.

Sexual Competitiveness and Induced Egg Sterility by Aedes aegypti and Aedes albopictus Gamma-Irradiated Males: A Laboratory and Field Study in Mexico.

The sterile insect technique may prove useful for the suppression of mosquito vectors of medical importance in regions where arboviruses pose a serious public health threat. In the present study, we examined the effects of sterilizing irradiation doses across different ratios of fertile:irradiated males on the mating competitiveness of Ae. aegypti and Ae. albopictus under laboratory and field-cage conditions. For both species, the percentage of females inseminated and the number of eggs laid over two gonotrophic cycles varied significantly in mating treatments involving 1:1, 1:5, and 1:10 fertile:irradiated males compared to controls of entirely fertile or entirely irradiated males but was not generally affected by the irradiation dose. Egg hatching was negatively affected in females exposed to increasing proportions of irradiated males in both laboratory and field cages. Male competitiveness (Fried's index) values varied from 0.19 to 0.58 in the laboratory and were between 0.09 and 1.0 in field cages, depending on th species. Competitiveness values were negatively affected by th eirradiation dose in both species under field-cage conditions, whereas in the laboratory, Ae. albopictus was sensitive to the dose but Ae. aegypti was not. In general, male competitiveness was similar across all mating regimes. Most importantly, induced egg sterility was positively correlated with the proportion of irradiated males present in the mating treatments, reaching a maximum of 88% under field-cage conditions for both Ae. aegypti and Ae. albopictus males treated with 50 and 40 Gy irradiation, respectively. These results indicate that sterile males produced at our facility are suitable and competitive enough for field pilot SIT projects and provide guidance to decide the optimal sterile:fertile ratios.

Self-sustained oscillations and global climate changes.

The periodic changes of atmospheric CO2 and temperature over the last 5 Myr reveal three features that challenge current climate research, namely: (i) the mid-Pleistocene transition of dominant 41-kyr cycles to dominant 100-kyr cycles, (ii) the absence of a strong precession signal of approximately 20 kyr, and (iii) the cooling through the middle and late Holocene. These features are not directly addressable by Earth's orbital changes described by Milankovitch. Here we show that a closed photochemical system exposed to a constant illumination source can sustain oscillations. In this simple conceptual model, the oscillations are intrinsic to the system and occur even in the absence of periodic radiative forcing. With proper adaptations to the Earth system, this oscillator explains the main features of past climate dynamics. Our model places photosynthesis and the carbon cycle as key drivers of climate change. We use this model to predict the relaxation of a 1,000 PgC pulse of CO2. The removal of 50% of this CO2 will require one century, and will lead to a warmer and wetter future. However, more pronounced glaciation cycles emerge on the millennial timescale.

Homoclinic organization in the Hindmarsh-Rose model: A three parameter study.

Bursting phenomena are found in a wide variety of fast-slow systems. In this article, we consider the Hindmarsh-Rose neuron model, where, as it is known in the literature, there are homoclinic bifurcations involved in the bursting dynamics. However, the global homoclinic structure is far from being fully understood. Working in a three-parameter space, the results of our numerical analysis show a complex atlas of bifurcations, which extends from the singular limit to regions where a fast-slow perspective no longer applies. Based on this information, we propose a global theoretical description. Surfaces of codimension-one homoclinic bifurcations are exponentially close to each other in the fast-slow regime. Remarkably, explained by the specific properties of these surfaces, we show how the Hindmarsh-Rose model exhibits isolas of homoclinic bifurcations when appropriate two-dimensional slices are considered in the three-parameter space. On the other hand, these homoclinic bifurcation surfaces contain curves corresponding to parameter values where additional degeneracies are exhibited. These codimension-two bifurcation curves organize the bifurcations associated with the spike-adding process and they behave like the "spines-of-a-book," gathering "pages" of bifurcations of periodic orbits. Depending on how the parameter space is explored, homoclinic phenomena may be absent or far away, but their organizing role in the bursting dynamics is beyond doubt, since the involved bifurcations are generated in them. This is shown in the global analysis and in the proposed theoretical scheme.

Mechanical response of dense pedestrian crowds to the crossing of intruders.

The increasing number of mass events involving large crowds calls for a better understanding of the dynamics of dense crowds. Inquiring into the possibility of a mechanical description of these dynamics, we experimentally study the crossing of dense static crowds by a cylindrical intruder, a mechanical test which is classical for granular matter. The analysis of our experiments reveals robust features in the crowds' response, comprising both similarities and discrepancies with the response of granular media. Common features include the presence of a depleted region behind the intruder and the short-range character of the perturbation. On the other hand, unlike grains, pedestrians anticipate the intruder's passage by moving much before contact and their displacements are mostly lateral, hence not aligned with the forces exerted by the intruder. Similar conclusions are reached when the intruder is not a cylinder, but a single crossing pedestrian. Thus, our work shows that pedestrian interactions even at high densities (3 to 6 ped/m2) do not reduce to mechanical ones. More generally, the avoidance strategies evidenced by our findings question the incautious use of force models for dense crowds.

[Markers of thrombophilia in patients with retinal vein thrombosis]. / Determinación de factores trombofílicos en pacientes con trombosis venosas retinianas.

BACKGROUND: Thrombophilia is an alteration of hemostasis that increases the risk to venous or arterial thrombosis. This condition may be the underlying cause of retinal vein thrombosis. AIM: To study the presence of thrombophilia in patients with retinal vein thrombosis. PATIENTS AND METHODS: Prospective study of 55 patients aged 22 to 86 years, with retinal vein thrombosis (central or branch). Antithrombin III, coagulant protein C, functional protein S, resistance to activated C protein, homocysteine, prothrombin G20210A gene, lupus anticoagulant and anticardiolipin antibodies were measured in all. RESULTS: Seventeen patients had thrombophilic markers (antiphospholipid syndrome in seven, hyperhomocysteinemia in six and resistance to protein C in three). Of these 17 patients, 53% had high blood pressure, 35% an abnormal serum lipid profile and 23% a personal history of thrombosis. The thrombosis was central in 12 (ischemic in four) and of a branch in five (ischemic in two). CONCLUSIONS: Thrombophilic markers must be assessed in patients with retinal vein thrombosis.

Tratamiento del desprendimiento de retina por agujero macular con recambio de vítreo líquido por gas intravítreo / Treatment of retinal detachment by macular hole with liquid vitreous exchange by intravitreal gas

Se realiza la novedosa técnica del recambio de vítreo líquido por gas expansible, seguida de posición prona postoperatoria, en 17 pacientes con desprendimiento retinal por agujero macular en altos miopes. Se obtuvo éxito en 10 casos y otros 4 fueron exitosos a expensas de recurrir a la vitrectomía instrumental vía pars plana con inyección de gas preoperatoria. Se enfatiza los grandes beneficios operativos y funcionales de esta técnica

Alteraciones neuropsicológicas en lesiones bi-parieto-occipitales / Neuropsychological changes in bilateral parieto-occipital lesions

Se presentan 6 casos de lesiones bi-occipito-parietales, 5 de ellos de origen vascular; se detaca la existencia de 3 casos de hemorragias intracerebrales bilaterales simultáneas. El cuadro inicial fue de compromiso de conciencia (delirio agudo en uno de ellos) asociado a defecto visuales que llegaron hasta la ceguera cortical transitoria. Posteriormente se comprobaron múltiples defectos visulaes (agnosias, negligencia unilateral,alexias), del manejo de relaciones espaciales (apraxias constructivas, acalculias, desorientación derecha-izquierda, ataxia óptica de la mano, etc.) y de la memoria. Existen formas de transición entre la amnesia hipocámpica, las agnosias visuales y los síndromes bi-parieto-occipitales

Desprendimiento retinal por impacto de pelota grande / Retinal detachment by impact of a big soccer-ball

Se describen las características clínicas y los resultados quirúrgicos en un grupo de 41 pacientes con un desprendimiento retinal inducido por un pelotazo en el juego del fútbol (39 pacientes), baloncesto (1 paciente) y voleibol (1 paciente). El período de latencia entre el trauma y el desprendimiento retinal fue inferior a 1 semana en 18 casos, sugiriendo que los desgarros se generan en el momento del impacto La mayor parte de los pacientes presentaban diálisis y desgarros superotemporales. Desgarro en herradura sólo se observó en un ojo miope. El impacto provocó un desgarro retinal gigante en un ojo alto miope. Se obtuvo la reaplicación retinal quirúrgica en 38 de 41 casos (92.7%). 60% de los casos mostraron maculopatía de grado variable. La visión final fue inferior a 0.1 en 6 casos con retina aplicada. Estos casos presentaban un desprendimiento retinal muy antiguo o una severa maculopatía