Glass- and crystal-forming model based on a granular two-dimensional system.

We study a two-dimensional system of magnetic particles under an alternating magnetic field. The particles are settled on the surface of a negative lens where they tend to sediment toward the center due to gravity. The effective temperature is controlled by the intensity of the applied magnetic field. The system is cooled down from a gaslike state to a solidlike state at different rates. We observe that for some slow cooling rates the final configuration of system is a hexagonal compact arrange, while for the faster cooling rates the final configurations are glasslike states. We followed the time evolution of the system, which allows us to determine in detail changes in quantities such as the interparticle distance. We determine the glass transition temperature for different cooling rates, finding that such temperature increases as the cooling rate decreases, in contrast with some other glass-forming liquids.

Energy landscape of colloidal dumbbells in a periodic distribution of light.

Using a ray tracing calculation, the energy landscape of dumbbells, made of spherical colloidal particles, interacting with a periodic distribution of light is calculated. As shown previously [E. Sarmiento-Gomez, J. A. Rivera-Moran and J. L. Aruaz-Lara, Soft Matter, 2018, 14, 3684], planar aggregates of spherical particles adopt discrete configurations in such light distribution. Here we focus on the case of colloidal dumbbells both symmetric and asymmetric from an experimental and theoretical point of view. It has been shown that the direct calculation using the ray tracing approximation is in excellent agreement with the experiment in spite of the fact that the particles size and the wavelength of the trapping light are comparable. We also corroborate, at least for the more simple case of a single particle in a parabolic light distribution, that the simple method used here provides the same results as the more complex and general Lorenz-Mie approach giving a more simple yet reliable method for the calculation of the energy landscape of colloidal aggregates in periodic light distributions.

Single particle states of colloidal particles in 2D periodic potentials.

Colloidal particles when subjected to a periodic array of potential wells are observed to adopt discrete stable configurations depending on the particle size/array wavelength ratio. Experimentally, the configuration states are determined for singlets, doublets and triplets of identical spheres in a periodic array of traps. The energy landscape of a single spherical particle is obtained by considering the refraction of the incident light as it passes throughout the particle. Then, the energy of a dumbbell is determined as the superposition of two singlets. The energy of a triplet is calculated as the superposition of a dumbbell and a single particle. As it is shown here, this direct method predicts accurately the stable particle configurations as observed in the experiments. The method can be generalized to obtain the potential energy of an n-particle aggregate, using as building blocks the energies of singlets and doublets.

Brownian motion in non-equilibrium systems and the Ornstein-Uhlenbeck stochastic process.

The Ornstein-Uhlenbeck stochastic process is an exact mathematical model providing accurate representations of many real dynamic processes in systems in a stationary state. When applied to the description of random motion of particles such as that of Brownian particles, it provides exact predictions coinciding with those of the Langevin equation but not restricted to systems in thermal equilibrium but only conditioned to be stationary. Here, we investigate experimentally single particle motion in a two-dimensional granular system in a stationary state, consisting of 1 mm stainless balls on a plane circular surface. The motion of the particles is produced by an alternating magnetic field applied perpendicular to the surface of the container. The mean square displacement of the particles is measured for a range of low concentrations and it is found that following an appropriate scaling of length and time, the short-time experimental curves conform a master curve covering the range of particle motion from ballistic to diffusive in accordance with the description of the Ornstein-Uhlenbeck model.

Early intervention in pertussis outbreak with high attack rate in cohort of adolescents with complete acellular pertussis vaccination in Valencia, Spain, April to May 2015.

Forty-three pertussis cases reported in May 2015 in Valencia were linked to a school outbreak where 90% of the students had been vaccinated. Cases were diagnosed upon paediatrician consultation and in hospital emergency units. Approximately half of the cases were students born in 2002, the first age cohort with complete shift to acellular pertussis vaccine. Public health intervention, visiting school premises to conduct interviews, sample collection and early antibiotic prophylaxis stopped further spread in the community.

Brownian motion of optically anisotropic spherical particles in polymeric suspensions.

We studied the rotational and translational diffusion of optically anisotropic liquid crystal particles embedded in semidiluted polymer solutions of Poly-Ethylene-Oxide (PEO) at different concentrations and different molecular weights. The polymer radius of gyration was chosen to be similar to the size of the probe particles and the polymer concentrations used are just above the crossover concentration. Thus, the system consists of solid probe particles moving in a sea of overlapping particles of similar size. We found that the behavior of both particle dynamics, rotational and translational, is similar in the range of concentrations considered here. In both cases, two linear diffusive regimes are observed, separated by a subdiffusive time interval. The spatial scale at which this intermediate regime appears shows a dependence on both the polymer concentration and molecular weight, and has a value similar to the thickness of the polymer-depleted layer usually found in this kind of systems. Additionally, we observe that the colloidal dynamic scales with the overlapping degree of the polymer particles.

Transition from diffusive to subdiffusive motion in colloidal liquids.

In this work we report experimental and theoretical results for the motion of single colloidal particles embedded in complex fluids with different interparticle interactions. The motion of particles is found to follow a similar behavior for the different systems. In particular, the transition from the short-time diffusive motion to the subdiffusive intermediate-time motion is found to occur when the square root of its mean squared displacement is in the order of 1 tenth of the neighbors' interparticle distance, thus following a quantitative criterion similar to Lindemann's criterion for melting.

Multifractality in dilute magnetorheological fluids under an oscillating magnetic field.

A study of the multifractal characteristics of the structure formed by magnetic particles in a dilute magnetorheological fluid is presented. A quasi-two-dimensional magnetorheological fluid sample is simultaneously subjected to a static magnetic field and a sinusoidal magnetic field transverse to each other. We analyzed the singularity spectrum f(α) and the generalized dimension D(q) of the whole structure to characterize the distribution of the aggregates under several conditions of particle concentration, magnetic field intensities, and liquid viscosity. We also obtained the fractal dimension D(g), calculated from the radius of gyration of the chains, to describe the internal distribution of the particles. We present a thermodynamic interpretation of the multifractal analysis, and based on this, we discussed the characteristics of the structure formed by the particles and its relation with previous studies of the average chain length. We have found that this method is useful to quantitatively describe the structure of magnetorheological fluids, especially in systems with high particle concentration where the aggregates are more complex than simple chains or columns.

Lateral aggregation induced by magnetic perturbations in a magnetorheological fluid based on non-Brownian particles.

A study of lateral aggregation, induced by an oscillatory field, in a magnetorheological fluid based on non-Brownian magnetic particles is presented. We investigate the behavior of chains formed by the particles, due to the simultaneous application of a static magnetic field and a sinusoidal magnetic field transverse to each other. We show that the effective oscillating field enhances the aggregation process. We discuss this result in terms of an effective particle concentration induced by the oscillating field when chains oscillate angularly and sweep the area around them. The oscillating field produces a lateral aggregation similar to that observed in systems composed of Brownian particles which is induced by thermal fluctuations. We study the effect of the oscillating field on the angular amplitude described by single chains. It is observed that the angular amplitude decreases as the frequency of the oscillating field increases; we discuss this behavior numerically in terms of a simple model for this system. Lateral aggregation is studied in detail in isolated pairs of chains of equal length at several conditions of separation and displacement. From the results, a phase diagram is obtained showing the conditions under which aggregation is possible.

Hydrodynamic interactions between colloidal particles in a planar pore.

The correlation between the motion of pairs of colloidal particles confined in a planar pore is measured using optical microscopy. The systems studied here are aqueous suspensions of polystyrene spheres of diameter 1.9 µm, interacting as effective hard spheres, confined between two parallel planar plates separated by 2.9 µm. The lateral motion, along the plane parallel to the plates, of the particles is recorded with a time resolution of 30 frames s(-1). From the short-time motion, the hydrodynamic diffusion coefficients are determined as functions of the interparticle distance for various particle concentrations. At low concentrations, when the static correlation between particles is also low, the diffusion coefficients exhibit some symmetry, and at higher concentrations they are modulated by the structure of static correlation.

Colloidal diffusion inside a spherical cell.

The hydrodynamic hindering of a single-particle dynamics under total confinement is measured by optical microscopy. The three-dimensional trajectories of single-colloidal particles confined in spherical water globules of sizes only a few times the particle's diameter are tracked as they sample the entire volume of the globule. The hydrodynamic interactions between the particle and the spherical wall produce a dependence of the short-time diffusion on the particle's distance to the surface and an asymmetry in the radial and tangential components of the local diffusion coefficient, with the diffusion along the tangential direction being faster than along the radial direction. The latter decreasing close to the wall while the former being practically constant.

Comparative study of cerebral blood flow between postural tachycardia and neurocardiogenic syncope, during head-up tilt test.

We assessed the cerebral blood flow velocity response to head-up tilt test in patients with typical neurocardiogenic syncope compared with patients showing postural tachycardia. Fifty patients (21 men) with history of orthostatic intolerance, younger than 50 years (mean 27 +/- 10), participated in the study. Transcranial Doppler sonography of the middle cerebral artery, heart rate and brachial blood pressure were recorded during a head-up tilt test. According to the outcome of the test, patients were categorized in two groups: neurocardiogenic syncope (29 patients) and postural tachycardia (21 patients). The clinical history of the two groups was similar. During baseline in the supine position, no differences in haemodynamic parameters were observed. From the first min of tilt, the heart rate was higher in patients with postural tachycardia than in patients with neurocardiogenic syncope. Although, during tilt, the absolute values of the cerebral blood flow parameters were similar in the two groups, throughout tilt, continuous observation of the Doppler recording in patients with postural tachycardia showed intermittent fluctuation of the blood flow velocity, with an oscillatory pattern, which were not observed in the recordings in patients with neurocardiogenic syncope. Comparison of patients with neurocardiogenic syncope, and those with postural tachycardia also showed larger variations of the pulsatility index (P < 0.05) in the postural tachycardia group. These findings support the possibility that abnormalities within the central nervous system play a pivotal role in the pathogenesis of postural tachycardia.

Hydrodynamic interactions in quasi-two-dimensional colloidal suspensions.

The effects of the hydrodynamic interactions on the short-time dynamics of colloidal, hard-sphere-like particles confined between two parallel walls are measured by digital videomicroscopy. We find that such effects can be described in terms of an effective two-dimensional hydrodynamic function H(k), defined as a straightforward adaptation to two dimensions of the corresponding object describing collective dynamics for the three-dimensional (3D) suspensions. Interestingly, the behavior of H(k) is qualitatively similar to the hydrodynamic function of 3D suspensions of hard spheres. We also found that for values of k where the static structure factor is 1, the dynamics is determined only by self-diffusion.

[Outbreak of shigellosis in a lower-class district]. / Brote de shigellosis en un barrio de nivel social bajo.

BACKGROUND: The outbreaks of Shigella sonnei in our environment frequently involve day care centers and elementary schools. An outbreak of shigellosis in a lower-class district is reported. The purpose of this study is that of pinpointing the center of infection, the means of contagion, the characteristics of those infected and of assessing the suitability of the measures taken. METHODS: For monitoring the outbreak over time, a combined observational timeline study was conducted within a territory the bounds of which were marked by means of the conventional epidemiological monitoring variables (time, place and individual). The infectivity of the center of infection (contagion rate) is analyzed by age, gender and school; rate ratio and percentage attributable thereto. RESULTS: On a time-related basis, the outbreak in question started on week 46/97 and ended on week 8/98. This outbreak involved 218 individuals (110 males and 108 females) totaling 5.46% of the district. The highest frequency was found among the 0-4 age group (43.6%), 29.4% in day care (70.32% contagion rate) with a relative risk of 3.9 (95% CI: 2.57-5.93) and 74.36% attributable percentage. The rate ratio between day care and the schools in the district in question is 5.62 (95% CI: 4.33-7.31). Stool cultures were taken and analyzed in 84 cases (38.5%), Shigella sonnei being detected in 38 cases (17.4%). Antibacterial treatment (amoxicillin-clavulan) was set out and individual and group health and safety measures were employed. CONCLUSIONS: The long communicability period and the small number of viable microorganisms necessary for causing this disease fostered its being passed on from one person to another at school and in the home. The measures employed effectively confined the contagion of the infectious agent at the schools.

[School failure in a cohort of adolescents]. / Fracaso escolar en una cohorte de adolescentes.

OBJECTIVE: To evaluate a cohort of adolescents as to whether their personal characteristics and/or determined habits of health and social relations bore any relation to the state of their studies two years later. DESIGN: A prospective study following a cohort of adolescents. PARTICIPANTS AND SETTING: Third-year ESO (aged c. 14) adolescents from the four state secondary schools in Puerto de Sagunto. INTERVENTIONS: Once the cohort (n = 551) was defined, in November 1995 the students themselves filled in a questionnaire on health and relationship habits. Two years afterwards they were located through school registers and classified as good if they were in the appropriate year, repeat if they were repeating a year and disappeared if they had left school. These last two categories were both considered school failures (SF). MEASUREMENTS AND RESULTS: 222 students were classed as SF (40%). 118 of these (21.4%) had left and 104 (18.9%) were repeating a year. There were statistically significant differences in the following characteristics measured at the start of the study: greater SF among boys than girls (46.4%/35.6%): the disappeared had a higher average age than the good students (14.98/14.17), higher average number of siblings (2.73/2.26), and higher average of nights they went out during the week (1.65/0.84). Mean family income was lower in the repeat group (1926087/2475436 pesetas); the money students received weekly was higher in both SF groups (over 900/641 pesetas). Students whose fathers have university degrees made up only 7.4% of SF; and no student whose mother had a university degree was SF. 17.5% of those who said they spent their free time with their family were SF, whereas 53% of those who devoted their free time basically to enjoying themselves were SF. On drug consumption, those who replied they never smoked had 27.2% SF, never consumed alcohol 25.8% SF, never took marihuana 35.3% SF, and never consumed other drugs 39.5% SF. Students who said their relationships with family and teachers was bad had 70% and 62.2% of SF, respectively. 70% of those who felt depressed were SF. CONCLUSIONS: This study confirms that a favourable family atmosphere is important in preventing school failure. It also makes clear that young people's social relationships and health habits are closely associated to their being a standard student or a school failure.

[The evolution of health and relationship habits of an adolescent cohort of Puerto de Sagunto (1995-1996)]. / Evolución de hábitos de salud y de relación de una cohorte de adolescentes de Puerto de Sagunto (1995-1996). Grupo de Trabajo TBC-3. Valencia.

OBJECTIVE: To know the prevalence of tobacco consumption, alcohol and marihuana as well as the habits of relationship, in an adolescents cohort of 3rd of Obligatory Secondary Teaching (ESO), that accede for the first time to one of the four secondary school of Puerto de Sagunto and the evolution of these habits after a year of follow-up. DESIGN: Transverse observational study with data withdrawal in two moments. Site. In the four secondary school of Puerto de Sagunto (Valencia). PATIENT AND OTHERS PARTICIPANTS: Adolescent of 3rd of ESO that accede for the first time to the four secondary school of Puerto de Sagunto in the course 95-96. INTERVENTIONS: A self-fully validated habits poll of health and of relationship was given to the pupils of 3rd of ESO (n = 573), and a year after was given the same poll, to the pupils already in 4th of ESO (n = 395). MEASUREMENTS AND RESULTS: On health habits, were found meaningful statistic differences in various variables: in tobacco consumption several times to the month passes of the 30% to the 40%, in alcohol consumption more than proven passes of the 35% to the 52%, in have you intoxicated the response never passes of the 67% to the 57%, in the paragraph of marihuana consumption, the response never passes of the 82% to the 72%. On the habits of relationship were found significant statistic differences with respect to number of nocturnal exists during the week that goes from 1.07 to 1.33, the return hour before 10 passes of the 23% to the 8%, as well as the type of associations to those which belong, sports club passes of the 38% to the 46%. In the paragraph of relationship to their teachers, the response good passes of the 89% to the 93%. CONCLUSIONS: The step of 14 to 15 years supposes in this population an increase in alcohol consumption, tobacco and marihuana, they go out more days at night and return later to house, are associated more in sports clubs and have better relationships to their teachers. The knowledge of these habits permits the intervention with preventive programs, that attempt to change attitudes toward these toxic habits and to promote the healthiest.

[The evolution of pulmonary tuberculosis in health area no 4 in Valencia during the period 1988-1993]. / Evolución de la tuberculosis pulmonar en el área de salud 4 de Valencia durante el peródo 1988-1993.

BACKGROUND: Morbidity from Pulmonary tuberculosis, detected by the system EDO in the Autonomous Community of Valencia, shows an increasing trend and differential behaviour in relation with age and constitutes, with no doubt, a Public Health problem involving a joint action of multiple clinical care and preventive units. METHODS: In our study, the cases of notified and confirmed pulmonary tuberculosis over the period 1988-1993 in the Health Area number 4 (Region Camp de Morvedre 167.744 inhabitants) are analyzed by estimating the evolution of incidence, the diagnosis time and place where this diagnosis was made in accordance with the conventional variables of ecological studies and excluding from our registry the cases of those patients with co-infection by virus VIH. RESULTS: The growing evolution of incidence, the mean rate for the period (49.95.10(5) h.), the rate differential per age-groups during the period and the concentration of cases in the young age-groups (15-39 years) constitute, together with the diagnosis time (75.6 days in Primary Health Care; 74.3 in Hospital), the most outstanding results. Nevertheless, the prolongation of the diagnosis time for order age-groups (140-168 days in people older than 54 years) and the absence of a previous known contact, suggest the presence of undetected cases of TBC and dissemination ways other than the interfamily ones. CONCLUSIONS: An improved notification and identification of cases from hospital sources involves the necessity of reducing the mean diagnosis time and the research on the ways of transmission other than the interfamily ones; this explains a limited part of the incidence.

[Gastroenteritis outbreak associated with water consumption, possibly caused by Norwalk or Norwalk-like virus]. / Brote de gastroenteritis asociado al consumo de agua, posiblemente producido por virus tipo Norwalk o semejantes.

BACKGROUND: It is described an acute gastroenteritis outbreak of probable hydric transmission in Ontinyent (Valencia). It was declared on the 31st of January, 1992 and affected 3541 people according to the declaration done by the sanitary services who attended the patients. The clinical situation was characterized by the presence of profuse and watery diarrhoea, nausea, vomiting, abdominal pain and fever or febricula. METHODS: A preliminary study of the cases has been done, the information being treated with the classical method of descriptive epidemiology and a later study of the transversal observation type by means of a telephone inquiry. RESULTS: The results show that this outbreak affected approximately to a 30% of the population, and show the relation between consumption of water from the municipal water system and the outbreak, as well as the existence of a control population not affected for receiving a different water supply. CONCLUSION: Once rejected the bacterial origin for the results of the copro-cultivation done the analysis of the clinical and epidemiological characteristics of the outbreak, show a total agreement with the criteria described by Kaplan to characterize acute gastroenteritis outbreaks because of Norwalk-like virus.