Confined sandpile in two dimensions: Percolation and singular diffusion.

We investigate the properties of a two-state sandpile model subjected to a confining potential in two dimensions. From the microdynamical description, we derive a diffusion equation, and find a stationary solution for the case of a parabolic confining potential. By studying the systems at different confining conditions, we observe two scale-invariant regimes. At a given confining potential strength, the cluster size distribution takes the form of a power law. This regime corresponds to the situation in which the density at the center of the system approaches the critical percolation threshold. The analysis of the fractal dimension of the largest cluster frontier provides evidence that this regime is reminiscent of gradient percolation. By increasing further the confining potential, most of the particles coalesce in a giant cluster, and we observe a regime where the jump size distribution takes the form of a power law. The onset of this second regime is signaled by a maximum in the fluctuation of energy.

Análisis electroencefalográfico de la conectividad funcional en habituación por teoría de gráficas / Electroencephalographic analysis of the functional conectivity in habituation by graphics theory

Resumen Se ha propuesto, en la literatura de neurociencias, la hipótesis de que el cerebro funciona con base en redes glioneuronales, responsables de los procesos sensoriales, motores y cognitivos. La teoría de gráficas ofrece modelos matemáticos para describir estas redes complejas a partir de simples abstracciones: nodos y aristas. En este trabajo se plantea el uso de técnicas de procesamiento de señales para el análisis de la conectividad funcional entre ensambles neuronales a partir de medidas derivadas del EEG a través de la teoría de gráficas. Se describen los procedimientos para el análisis de la conectividad, desde el procesamiento y acondicionamiento de los registros, el cálculo de la densidad espectral en el EEG en banda ancha, la determinación de medidas de conectividad entre electrodos, y la estimación de parámetros de las redes complejas resultantes. Se analizó el EEG de 50 sujetos en intervalos de antes (Pre) y durante la fotoestimulación repetida (Rph). Con base en la significancia estadística de la respuesta durante Rph de desincronización/sincronización (D/S) en la banda alfa, y su extensión en las regiones corticales, los participantes se separaron en tres grupos: G1, G2 y G3. La pendiente de la regresión lineal D/S vs repetición en banda alfa, fue significativa en 16 de 16 regiones en G1, 12 de 16 en G2 y 5 de 16 en G3. La conectividad funcional siguió estos cambios mientras que en las bandas delta, theta y beta no se registraron modificaciones. D se relaciona con activación y la S con inhibición lo que apoya la hipótesis de la participación de alfa en el proceso cognitivo de habituación a la fotoestimulación.

Abstract The hypothesis that the brain works using glial-neuronal networks that are responsible for sensory, motor and cognitive processes has been proposed in the neuroscience literature. Graph theory offers mathematical models to describe these complex networks from simple abstractions such as nodes and connecting edges. In this work, usign signal processing techniques to the analysis of functional connectivity between neuronal emsembles derived from EEG measurements through theory graph. Procedures for the analysis of connectivity are described, from multichannel record processing and conditioning, computation of wideband power spectral density, determination of connectivity measures between electrodes, and parameter estimation of the resulting complex networks. EEG recordings from fifty subjects were analyzed in intervals before (pre) and during repeated photostimulation (Rph). Based on the statistical significance of the response during Rph, desynchronization/synchronization (D/S) in alfa band, and its wide distribution in corticals areas, the participants were divided into three groups: G1 , G2 and G3. The slope D/S in alfa band was significant in 16 of 16 regions (G1), 12 of 16 (G2) and 5 of 16 (G3). The functional connectivity depicted the same trend as these changes, whereas in the delta, theta and beta bands occurred no modifications. D is related to activation and S with inhibition, supporting the hypothesis of alfa-band's participation in the cognitive process of habituation to photostimulation.

Participation of protein kinases and phosphatases in the progesterone-induced acrosome reaction and calcium influx in human spermatozoa.

In human spermatozoa, protein kinases have a role in the acrosome reaction (AR) induced by a variety of stimuli. However, there is disagreement or a lack of information regarding the role of protein kinases and phosphatases in the progesterone (P)-induced increase in intracellular calcium concentration ([Ca2+ ]i ). In addition, there are no studies regarding the role of Ser/Thr and Tyr phosphatases and there are contradictory results regarding the role of Tyr kinases in the P-induced acrosome reaction. Here, we performed a simultaneous evaluation of the involvement of protein kinases and phosphatases in the P-induced acrosome reaction and in the P-induced calcium influx. Motile spermatozoa were capacitated for 18 h and different aliquots were allocated to treated or control groups and then evaluated for their ability to undergo the acrosome reaction and to increase [Ca2+ ]i in response to P. The acrosome reaction was evaluated using Pisum sativum agglutinin (PSA)-FITC, and [Ca2+ ]i was evaluated using fura 2AM. At all of the concentrations tested, PKA inhibitors significantly reduced the percentage of the P-induced acrosome reaction (p < 0.001). However, only the highest concentrations of PKA inhibitors reduced the P-induced calcium influx; lower concentrations of PKA inhibitors did not affect it. Similar results were apparent for PKC inhibitors and for tyrosine kinase inhibitors. None of the Ser/Thr phosphatase inhibitors affected the P-induced acrosome reaction or the P-induced calcium influx, except for the PP2B inhibitors that significantly reduced the P-induced acrosome reaction without affecting calcium influx. Finally, the protein tyrosine phosphatase inhibitors significantly blocked the P-induced acrosome reaction and reduced the amplitude of the P-induced calcium transient (p < 0.001) as well as the amplitude of the plateau phase (p < 0.01). The data suggest that protein kinases and possibly PP2B have a role on the acrosome reaction at some point downstream of calcium entry and that Tyr phosphatases have a role on the acrosome reaction upstream of calcium entry.

Fragmentation processes in two-phase materials.

We investigate the fragmentation process of solid materials with crystalline and amorphous phases using the the discrete element method. Damage initiates inside spherical samples above the contact zone in a region where the circumferential stress field is tensile. Cracks initiated in this region grow to form meridional planes. If the collision energy exceeds a critical value which depends on the material's internal structure, cracks reach the sample surface resulting in fragmentation. We show that this primary fragmentation mechanism is very robust with respect to the internal structure of the material. For all configurations, a sharp transition from the damage to the fragmentation regime is observed, with smaller critical collision energies for crystalline samples. The mass distribution of the fragments follows a power law for small fragments with an exponent that is characteristic for the branching merging process of unstable cracks. Moreover this exponent depends only on the dimensionally of the system and not on the microstructure.

The expression of p73 in the organum vasculosum of the lamina terminalis and choroid plexus of spontaneously hypertensive rats.

The p73 proteins are present in different kinds of cells of the central nervous system, such as the choroid plexus, circumventricular structures and neuroepithelium. It has been reported that spontaneously hypertensive rats show ventricular dilation, changes in cerebrospinal fluid proteins and variations in the circumventricular structures such as the organum vasculosum of the lamina terminalis and the choroid plexus, which are altered in ventricular dilation. The aim of the present work is to study p73 expression in the organum vasculosum of the lamina terminalis and the choroid plexus and its variations in high blood pressure. Brains from control Wistar-Kyoto rats and spontaneously hypertensive rats were used. The organum vasculosum of the lamina terminalis and the choroid plexus were processed by immunohistochemistry and western blot with anti-TAp73. We found weaker markings in the organum vasculosum of the lamina terminalis and stronger markings in the choroid plexus of the hypertensive than the control rats. Therefore, hypertension in the spontaneously hypertensive rats produces alterations in choroid plexus protein p73 expression that is similar to that described for other circumventricular organs, but it is different in the organum vasculosum of the lamina terminalis. We can conclude that the functional balance between p73, organum vasculosum of the lamina terminalis and choroid plexus, which is probably necessary to maintain the normal functioning of these structures, is altered by the hypertension found in these rats.

Scaling laws for impact fragmentation of spherical solids.

We investigate the impact fragmentation of spherical solid bodies made of heterogeneous brittle materials by means of a discrete element model. Computer simulations are carried out for four different system sizes varying the impact velocity in a broad range. We perform a finite size scaling analysis to determine the critical exponents of the damage-fragmentation phase transition and deduce scaling relations in terms of radius R and impact velocity v(0). The scaling analysis demonstrates that the exponent of the power law distributed fragment mass does not depend on the impact velocity; the apparent change of the exponent predicted by recent simulations can be attributed to the shifting cutoff and to the existence of unbreakable discrete units. Our calculations reveal that the characteristic time scale of the breakup process has a power law dependence on the impact speed and on the distance from the critical speed in the damaged and fragmented states, respectively. The total amount of damage is found to have a similar behavior, which is substantially different from the logarithmic dependence on the impact velocity observed in two dimensions.

Comparación y manejo de los diferentes riesgos el agua, en los aspectos social, económico y de la salud general / Comparison and aanagement of different water-reated risks, including social, eeconomic and health aspects

El agua en exceso o déficit es perjudicial para los seres vivos y para el desarrollo social y económico de las comunidades. Desastres naturales relacionados con el agua, como las inundaciones y los maremotos son dos ejemplos claros de catástrofes relacionadas con el agua que pueden afectar seriamente el desarrollo integral de ciudades y países, en cualquier esfera productiva. Además de los daños en la actividad económica o en el aspecto social y habitacional, el agua presenta un gran riesgo para las comunidades desde el punto de vista de la salud en general. El agua no potable, la cual desafortunadamente se consume en muchas naciones del mundo, es causante de gran cantidad de enfermedades en pacientes de todas las edades, viéndose más afectada la comunidad infantil de los países en vías de desarrollo. Considerando que en contra del agua y los desastres naturales la fortaleza humana es débil; sí se debe tener claro que hay muchas otras instancias y acciones que las comunidades pueden ejecutar con el objetivo de mitigar daños que tengan relación con el agua, la salud general y el desarrollo de las poblaciones. El manejo e identificación de las posibilidades para mejorar las anteriores situaciones negativas deben ser producto de la acción y trabajo en conjunto de las administraciones, la academia y los sectores privados, en busca de un beneficio general e integral.

Excess or deficit of water affects living beings, as well as social and economical development inof communities. Natural disasters related to water, such as flooding and tsunamis are two clear examples of risks catastrophes to influencing integral development of cities and countries at any productivity level. Besides the damage to economical, social or constructing aspects, water threatens general health in different communities, from the general health point of view. Non-potable water, which unfortunately is drank in many countries, causes great variety of diseases in patients of all ages, drastically affecting more drastically infants in underdeveloped countries. Considering that against water and natural disasters, humans men is are not strong enough; it is necessary to highlight that in other cases there are many actions communities can undertake to diminish water -related damage, health risks and general development. Identifying and managing different possibilities to improve these negative situations is must be the result of a joint effort that includes public administration, the academic area and all private institutions in order aware of the need and aiming to achieve a general and integral benefit.

Reissner's fibre proteins and p73 variations in the cerebrospinal fluid and subcommissural organ of hydrocephalic rat.

Reissner's fibre (RF) is formed by the polymerization of the glycoprotein secreted by the subcommissural organ (SCO). The SCO also secretes soluble glycoprotein into the cerebrospinal fluid (CSF); variations in RF and SCO have been reported in hydrocephalus. On the other hand, hydrocephalus and other brain alterations have been described in p73 mutant mice. The p73 belongs to the tumour suppressor p53 protein family and has two isoforms: the TAp73 with apoptotic activity and DeltaNp73 with anti-apoptotic function. Moreover, the TAp73 isoform is glycosylated and secreted into the CSF. In the present work, we analysed the variations in RF and p73 proteins in the CSF and SCO of spontaneously hydrocephalic rats. Brains from control rats and spontaneously hydrocephalic rats of 12 months of age were used. The SCO sections were immunohistochemically processed with anti-TAp73 and anti-Reissner fibre (AFRU). The spontaneous hydrocephalus presents a decrease in the AFRU immunoreactive material in the SCO and an absence of RF. The anti-TAp73 was also present, slightly decreased, in the hydrocephalic SCO. AFRU and p73 bands were also detected in the CSF by western blot and six AFRU and p73 protein bands of a similar molecular weight were found in the CSF of the control rats. The number of AFRU and p73 bands was lower in the hydrocephalic rats than in the control rats. In conclusion, hydrocephalus produces a decrease in the secretions of the SCO and an absence of RF and a decrease in p73 and RF proteins in the CSF.

Fragmentation processes in impact of spheres.

We study the brittle fragmentation of spheres by using a three-dimensional discrete element model. Large scale computer simulations are performed with a model that consists of agglomerates of many particles, interconnected by beam-truss elements. We focus on the detailed development of the fragmentation process and study several fragmentation mechanisms. The evolution of meridional cracks is studied in detail. These cracks are found to initiate in the inside of the specimen with quasiperiodic angular distribution. The fragments that are formed when these cracks penetrate the specimen surface give a broad peak in the fragment mass distribution for large fragments that can be fitted by a two-parameter Weibull distribution. This mechanism can only be observed in three-dimensional models or experiments. The results prove to be independent of the degree of disorder in the model. Our results significantly improve the understanding of the fragmentation process for impact fracture since besides reproducing the experimental observations of fragment shapes, impact energy dependence, and mass distribution, we also have full access to the failure conditions and evolution.

Universality behind Basquin's Law of Fatigue.

Basquin's law of fatigue states that the lifetime of the system has a power-law dependence on the external load amplitude, tf approximately sigma 0- alpha, where the exponent alpha has a strong material dependence. We show that in spite of the broad scatter of the exponent alpha, the fatigue fracture of heterogeneous materials exhibits universal features. We propose a generic scaling form for the macroscopic deformation and show that at the fatigue limit the system undergoes a continuous phase transition. On the microlevel, the fatigue fracture proceeds in bursts characterized by universal power-law distributions. We demonstrate that the system dependent details are contained in Basquin's exponent for time to failure, and once this is taken into account, remaining features of failure are universal.

Computer simulation of fatigue under diametrical compression.

We study the fatigue fracture of disordered materials by means of computer simulations of a discrete element model. We extend a two-dimensional fracture model to capture the microscopic mechanisms relevant for fatigue and we simulate the diametric compression of a disc shape specimen under a constant external force. The model allows us to follow the development of the fracture process on the macrolevel and microlevel varying the relative influence of the mechanisms of damage accumulation over the load history and healing of microcracks. As a specific example we consider recent experimental results on the fatigue fracture of asphalt. Our numerical simulations show that for intermediate applied loads the lifetime of the specimen presents a power law behavior. Under the effect of healing, more prominent for small loads compared to the tensile strength of the material, the lifetime of the sample increases and a fatigue limit emerges below which no macroscopic failure occurs. The numerical results are in a good qualitative agreement with the experimental findings.

Counterion correlations and attraction between like-charged macromolecules.

A simple model is presented for the appearance of attraction between two like-charged polyions inside a polyelectrolyte solution. The polyions are modeled as rigid cylinders in a continuum dielectric solvent. The strong electrostatic interaction between the polyions and the counterions results in counterion condensation. If the two polyions are sufficiently close to each other their layers of condensed counterions can become correlated resulting in attraction between the macromolecules. To explore the counterion induced attraction we calculate the correlation functions for the condensed counterions. It is found that the correlations are of very short range. For the parameters specific to the double stranded DNA, the correlations and the attraction appear only when the surface-to-surface separation is less than 7 A.

[Cerebral metabolic monitoring experience in critical neurological patients]. / Experiencia en monitorización metabólico-cerebral en pacientes críticos neurológicos.

BACKGROUND: Cerebral metabolic monitoring in critical neurological patients allows the assessment of neuronal tissue response to injury and to plan the best therapy to correct each critical brain situation. AIM: To evaluate the usefulness of cerebral metabolic monitoring in patients with acute cerebral injury. PATIENTS AND METHODS: A retrospective analysis of 29 patients with acute brain injury, in whom a catheter was located in the bulb of the jugular vein to perform a cerebral metabolic monitoring. These patients were compared with others that were not subjected to this monitoring. The evolution at six months of follow up was assessed using the Glasgow outcome score, considering a favorable evolution when this score was 4 or greater. RESULTS: Patients with an hyperemic state on admission or after optimization of therapy did not have hospital mortality, and 73% had Glasgow outcome score of 4 or greater at six months of follow up. On the other hand, 50% of those with hypoperfusion or global ischemia died during hospitalization and 72% had a Glasgow outcome score of 3 or less at six months. Patients not subjected to cerebral metabolic monitoring behave as those with hypoperfusion or global ischemia. CONCLUSIONS: Cerebral metabolic monitoring is an useful tool to optimize the management of patients with acute cerebral injury, and those patients with an hyperemic cerebral state have the best prognosis.

[Efficiency of oxidant gas generator cells powered by electric or solar energy]. / Eficiencia de celdas generadoras de gases oxidantes alimentadas con energía eléctrica o solar.

Diseases caused by microbial contaminants in drinking water continue to be a serious problem in countries like Mexico. Chlorination, using chlorine gas or chlorine compounds, is one of the best ways to treat drinking water. However, difficulties in handling chlorine gas and the inefficiency of hypochlorite solution dosing systems--due to sociopolitical, economic, and cultural factors--have reduced the utility of these chlorination procedures, especially in far-flung and inaccessible rural communities. These problems led to the development of appropriate technologies for the disinfection of water by means of the on-site generation of mixed oxidant gases (chlorine and ozone). This system, called MOGGOD, operates through the electrolysis of a common salt solution. Simulated system evaluation using a hydraulic model allowed partial and total costs to be calculated. When powered by electrical energy from the community power grid, the system had an efficiency of 90%, and in 10 hours it was able to generate enough gases to disinfect about 200 m3 of water at a cost of approximately N$8 (US $1.30). When the electrolytic cell was run on energy supplied through a photoelectric cell, the investment costs were higher. A system fed by photovoltaic cells could be justified in isolated communities that lack electricity but have a gravity-fed water distribution system.

[Exercise test in young steers at 2800 M above sea level]. / Pruebas de esfuerzo en banda sin-fin en jóvenes a 2800 m SNM.

Among its different activities the Mexican Health Ministry (SSA) promotes: 1) the specification of biological standards for the Mexican population; 2) mechanisms for early detection of physiopathological changes and 3) development of the appropriate technology as a basis for primary health care. As part of this program we studied a random sample of students at the "Colegio de Bachilleres" of Cuajimalpa a suburban area of Mexico City, situated at 2800 m above sea level, part of the equipment used was produced at the Center for Development and Technological Applications (CE-DAT), an agency of SSA. Height, weight, heart rate (HR), systolic and diastolic blood pressures (SBP/DBP) were measured at rest in sitting position, standing up and walking on a treadmill. The results show a population with similar physical characteristics to those described for other populations in Mexico, with HR values within a homogeneous distribution, except for three subjects with rates larger than 2 standard deviations (SD). At standing up, women showed an orthostatic reflex of 27 beats/min and men of 22 beats/min. At the beginning of the exercise, the HR curve becomes more homogeneous, showing a discrete ascending slope with a low correlation coefficient, suggesting low physical capacity of the studied population. As exercise continued, some subjects showed a low increment of HR, giving values differing by 2 SD. Five women and three men had resting SBP values lying 2 SD out of the mean values of the sample. During exercise, SBP increases 28 mmHg as average. Notwithstanding the low cardiac response, the time spent on the treadmill lies within the levels considered as good and, even, excellent, on the table of the National Institute of Cardiology. We discuss new procedures to analyze instantaneously the HR and the pressoreceptor reflex as well as their functional significance.

[Evaluation of heart rate and blood pressure in residents of Milpa Alta, D.F]. / Evaluación de la frecuencia cardiaca y presión arterial en habitantes de Milpa Alta, D.F.

Both the altitude of Mexico City (D.F.) and the increase in atmospheric pollutants make it important to establish parameters of comparison for cardiovascular variables, such as heart rate (HR) and blood pressure (BP). The epidemiological transition occurring in Mexico is increasing the need for human and physical resources at the first level of health care in order to perform early diagnoses of cardiovascular disorders among the population. Heart rate, systolic and diastolic blood pressures (SBP, DBP) were recorded under diverse conditions (seated, standing, performing 30 sit-ups, and then standing and seated after the sit-ups) in 235 inhabitants of Milpa Alta (a suburb of Mexico City). The procedures and equipment used were designed and produced at the Center for Development and Technological Applications, Ministry of Health. The following results were found: HR decreases with age and body surface. Likewise, the HR increase due to exercise is lower with increasing age and larger body surface and its return to resting levels is slower. SBP and DBP magnitude is directly related to body surface. In women an increase of body weight was found to be significantly related to a higher SBP. The orthostatic reflex (OR) decreases with age and body surface. The descending slope is higher in women than in men. We propose that the study of OR could provide better information for predicting cardiovascular changes. The described procedures can be performed with the physical and human resources available at the Health Centers. The extension of this type of applied research to first level health care centers would allow the country to respond efficiently to the epidemiological transition.

Installation of a water disinfection system in a Mexico City hospital.

With a view to evaluating a small-scale water disinfection system based on production and application of oxidizing gases, the level of equivalent residual chlorine and the degree of contamination by fecal and total coliform bacteria was assessed at various points in the drinking water system of a Mexico City hospital before and after installation of the disinfection equipment. Tests done in May and June 1989, prior to installation of the equipment, showed that residual chlorine concentrations were lower than the national standard in most of the samples and that a sizable portion of these samples were also contaminated with fecal and total coliform concentrations exceeding national standards. After installation of the disinfection system at the main inflow to the hospital's drinking water supply in August 1989, the equivalent residual chlorine concentrations were found adequate and no coliform bacteria were detected. These results indicate that the oxidant mixture generated by the newly installed system was effectively disinfecting the water.

Medición de la frecuencia cardiaca y presión arterial en habitantes del Ajusco, Tlalpan, Distrito Federal, México, utilizando equipo CEDAT / Measurement of cardiac frecuency and blood lpressure in a district of Mexico City

Para mejorar los procedimientos de atención de la salud cardiovascular en México es indispensable que en los centros de salud puedan hacer mediciones precisas con aparatos adecuados y se cuente con valores estándar de la población. Se analizaron en 102 personas la frecuencia cardiaca (FC), presión arterial sistólica (PAS) y presión arterial diastólica (PAD) en situasión de reposo sentados, parados, haciendo 30 sentadillas y nuevamente en reposo, parados y sentados. Se encontró una relación directa entre la magnitud de FC y PA con la supérficie corporal y con la edad cronológica. El reflejo ortostático va disminuyendo en relación con el incremento de años de vida. El ejercicio físico incrementó la FC, PAS y PAD que vuelve a disminuir en los siguientes cuatro a ocho minutos consecutivos al ejercicio en las personas en las tres primeras décadas de vida, mientras que en las otras dos no regresa, dentro de este tiempo, a los valores previos. Este decremento de RO es más pronunciado en los hombres que en las mujeres, aunque las cifras de PA son mayores en mujeres en las dos últimas décadas estudiadas. La distribución de los datos parece seguir la curva de distribución normal y queda dentro de lo descrito para altitudes sobre el nivel del mar menores que la ciudad de México. Al implantar los sistemas de medición que se describen en este trabajo, se podrán detectar al inicio los procesos patológicos que afecten la actividad cardiaca y la presión arterial, en situasiones de alteración del ambiente

To improve theprocedures for cardiovascular health care in Mexico it is necessary to be able to perform accurate measurements of the cardiovascular parameters with appropriate equipment and to count with standard values for the Mexican population at the primary health level. Cardiac frequency (CF), systolic arterial pressure (DAP) and diastolic arterial pressure (DAP) were analyzed in 02 consenting volunteers under resting (seated) and standing conditions as well as during excercise (30 sitting), and again after excercise under resurge conditions. A direct relation was found between CF, SAP and DAP with body surface and age. The orthostatic reflex (OR) diminished with age. Excercise increased FC, PAS and PAD, which decreased four-eight minutes after completing the excercise in those subjetcs under 30 years of age, where as in those aged 30 to 50 years these parameters did not return to their previous values. The RO decrement is more pronounced in men, although arterial pressure values ar higher in women aged 30 to 50 years. Data followed normal distribution curve, agreeing with the data re ported for altitudes lower than that of Mexico City. Implementing the measurement systems described in thi paper will allow early detection of pathology that migh affect cardiac activity and arterial pressure that could b, related to environmental pollution at the first level o medical attention.